Cutaneous laser surgery

Current Problems in

rmatology Volume 10 Number 4 July/August 1998

Cutaneous Laser Surgery '11

Alexander J. Stratigos, MD Maria Beatrice Alora, MD

Sandy Urioste, MD Jeffrey S. Dover, MD, FRCPC Department of Dermatology Beth Israel Deaconess Medical Center Harvard Medical School Boston, Massachusetts

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Current Problems in

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Cutaneous Laser Surgery B.

Commentary

130

Abstract

132

Introduction

132

Laser Physics Electromagnetic Radiation Principles of Laser Generation Laser Construction Properties of Laser Light Laser-Time Dependence Radiometry Skin Optics Laser-Tissue Interaction Selective Photothermolysis

133 133 133 133 133 134 134 136 136 138

Laser Safety

139

Lasers for Vascular Lesions Types of Lasers Clinical Applications

140 141 144

Lasers for Pigmented Lesions Types of Lasers Clinical Applications

148 149 151

Lasers For Skin Resurfacing Carbon Dioxide Laser Erbium:YAG Laser

154 154 160

Other Cutaneous Conditions for Which Lasers Are Useful Hypertrophic Scars and Keloids Striae Warts Hair Removal

162 163 164 164 165

Future Directions

167

References

168

Curr Probl Dermatol, July/August 1998

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Commentary It is a privilege to write a commentary to accompany the superb article on laser surgery by Stratigos et al. The senior author, Jeff Dover, has had a long interest in lasers and has been an integral participant in the development of new technology and new applications for existing technology. Dr. Dover is a regular instructor at the annual and midyear meetings of the American Academy of Dermatology. This article explains in a clear and concise manner the issues of physics of lasers--the basic science behind lasers, the uses of lasers for cutaneous diseases or for cosmetic improvements, and the directions that might occur in the near and distant future. Furthermore, the article provides sound information on the current limitations of lasers, which should aid in appropriate patient selection. Readers will find the treatise helpful in practice regardless of whether they use lasers. Jeffrey P. Callen, MD Editor-in-Chief

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Curr Probl Dermatol, July/August 1998

II

Alexander Stratigos, MD, obtained his medical degree in 1989 from the University of Athens in Athens, Greece. He served a medical internship at the Massachusetts General Hospital, Harvard Medical School, and a dermatology residency at the Department of Dermatology, Harvard Medical School. He is currently a Fellow in Laser Surgery at the Department of Dermatology, Beth Israel Deaconess Medical Center. He is a recipient of the "A. Onassis" scholarship on Photomedicine.

Maria Beatrice Alora, MD, obtained her medical degree in 1990 at the University of Santo Tomas in Manila, Philippines. She served her medical internship at the Philippine General Hospital in Manila, Phillipines, and her dermatology residency at the University of Santo Tomas in Manila, Philippines. She did a fellowship in Photomedicine at the Massachusetts General Hospital, Harvard Medical School in 1996 and is currently a Fellow in Laser Surgery in the Department of Dermatology, Beth Israel Deaconess Medical Center.

Sandy Urioste, MD, obtained her medical degree from Harvard Medical School in 1994 and did a pediatric internship at Boston's Children's Hospital. She is currently the chief resident in the Department of Dermatology of Harvard Medical School. At the completion of her residency, Dr. Urioste will be the Laser Fellow of the Department of Dermatology, Beth Israel Deaconess Medical Center.

Jeffrey S. Dover, MD, FRCPC, graduated magna cum laude with an MD degree from the University of Ottawa. His dermatology training was received at the University of Toronto, followed by research fellowships at St. John's Hospital for Diseases of the Skin at the University of London in London, United Kingdom, and a 2-year photomedicine fellowship at the Beth Israel Hospital and the Massachusetts General Hospital of Harvard Medical School. Dr. Dover is Associate Chairman, Department of Dermatology, Beth Israel Deaconess Medical Center and Associate Professor of Clinical Dermatology at Harvard Medical School. He also codirects the Harvard Medical Faculty Physicians Cosmetic Surgery and Laser Center at Beth Israel Deaconess Medical Center. Dr. Dover's research interests are photomedicine, lasers in medicine, cosmetic laser surgery, and medical education. Dr. Dover is author of more than 100 publications: articles, reviews, and book chapters, as well as several instructional audio and videotapes. He has coauthored two textbooks on cutaneous laser surgery, Illustrated Cutaneous Laser Surgery: A Practitioner's Guide and Lasers in Cutaneous and Aesthetic Surgery; and three other textbooks, two on general dermatology, Pocket Guide to Cutaneous Medicine and Surgery and Cutaneous Medicine and Surgery: Self Assessment and Review, and one for lay individuals, Skin Deep: An A to Z of Skin Disorders, Treatments and Health. Dr. Dover edits Journal Watch for Dermatology, a monthly abstracted journal by the Massachusetts Medical Society, publishers of the New England Journal of Medicine, and he is a member of numerous journal editorial boards. Dr. Dover serves on many committees including the Harvard Medical School Student Teaching Committee and the American Academy of Dermatology Committee for Guidelines of Care. Dr. Dover is actively involved in regional dermatologic societies. He is the past secretary and president of the New England Dermatological Society. He has organized and directed numerous medical conferences, including the Atlantic Dermatological Conference, the annual Harvard Medical School Continuing Medical Education Cutaneous Laser Surgery Course, New England Dermatological Society didactic meetings, national meetings on the practice of dermatology for graduating residents and for practicing dermatologists, and numerous courses at the annual meetings of the American Academy of Dermatology. Dr. Dover has received many honors including listings in the Who's Who of American Medicine and repeated nominations for the Teacher of The Year Award at Harvard Medical School.

Curr Probl Dermatol, July/August 1998

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II'

Cutaneous Laser Surgery More than 30 years of experience have resulted in advances of the technology, technique, and therapeutic efficacy of dermatologic lasers. The original lasers have been modified and improved, and new lasers with a more sophisticated technology have been introduced. Laser therapy has provided novel ways of treating difficult conditions and, for several skin diseases, it is now considered the treatment of choice. The goal of this article is to review laser physics and laser-tissue interactions, discuss the various groups of lasers and their clinical uses in dermatology, and to contemplate future developments in laser skin surgery. (Curr Probl Dermatol 1998;10:127-172.)

T

he concepts of laser radiation were first conceived by Albert Einstein who in 1917 published "The Quantum Theory of Radiation. "1 Einstein hypothesized that a photo n of electromagnetic energy could stimulate an "excited" atom with a corresponding transition energy, to emit another photon with the same energy. In 1958 the theory became reality when Schawlow and Townes, 2 working with microwaves, first proposed a technique for the generation of monochromatic radiation by stimulated emission. In 1960 Maiman 3 produced the first working laser consisting of a synthetic ruby surrounded by a helical flashlamp. The device was coined with the term LASER as an acronym for light amplification by stimulated emission of radiation. In the early 1960s Goldman et al4 used a ruby laser on human skin and demonstrated specific laser effects on various benign and epidermal lesions. His studies launched the era of lasers in clinical dermatology. Early in the 1970s lasers became widely used in dermatology with the advent of the argon, carbon dioxide, and neodymium:yttrium-aluminum-garnet (Nd:YAG) continuous-wave lasers. The argon laser emits light at 488 and 514 nm in the blue-green part of the visible light spectrum. It was initially used for the treatment of vascular lesions and port-wine stains with relatively good fading of the lesions but a rather high incidence of scarring, ranging from 4% to 15%. 5,6 The carbon dioxide laser emits light at 10,600 nm in the far

132

infrared region of the electromagnetic spectrum. It was used for controlled excision, vaporization, and coagulation of epidermal and dermal lesions such as verrucae, epidermal nevi, rhinophyma, and tattoos. Although controlled destruction was advantageous for several procedures, such as treatment of actinic cheilitis and periorbital syringomas, in many other cases there was no improved efficacy of this modality over conventional destructive techniques. 7 The Nd:YAG laser, emitting light at 1064 nm, was used with some success in the treatment of thick vascular lesions8; however, because of the deep and nonselective penetration of this laser, significant scarring was routinely seen. 9 The initial enthusiasm for the use of continuous-wave lasers waned because of relatively nonspecific tissue damage resulting in an increased frequency of textural changes and scarring after treatment. In 1983 Anderson and Parrish 1° introduced the theory of selective photothermolysis for producing selective tissue injury by laser light with the use of pulsed lasers. Selective photothermolysis greatly enhanced our understanding of laser-tissue interactions and led to a new generation of highly selective pulsed lasers that achieve specific and confined effects in tissue while minimizing collateral thermal damage. The development of new lasers was also boosted by technologic advances and the discovery of heavy metals and organic dyes as active media for the emission of light. The first pulsed laser introduced to dermatology was the flashlamp-pumped

Curr Probl Dermatol, July/August 1998

pulsed dye laser emitting at 577 rim, which was developed to treat vascular cutaneous lesions. Selective photothermolysis has been successfully applied in four general categories of skin diseases: (1) congenital and acquired vascular cutaneous lesions, (2) benign pigmented epidermal and dermal lesions and tattoos, (3) cutaneous resurfacing of photoaged skin and scars, and (4) a variety of miscellaneous areas including hair removal.

Loser Physics

Electromagnetic Radiation Electromagnetic radiation is a fundamental form of energy that exhibits properties of both waves and discrete packages of energy, called photons. Starting from the shorter wavelengths, electromagnetic radiation (EMR) includes x rays and gamma rays, ultraviolet radiation, visible light, infrared radiation, microwaves, and radiowaves (Fig. 1). The interaction of EMR and matter is mainly characterized by the absorption of energy and excitation of absorbing particles by photons. Short wavelength high-energy rays such as ionizing radiation (gamma rays and x rays) cause ionization of molecules in an indiscriminate fashion. Far-infrared energy heats biologic tissue and cannot be applied in a precise way. Most of the lasers used in dermatology fall in the visible and near-infrared wavelengths that lie between 400 and 10,600 nm. Although low-energy visible light irradiates our skin constantly without causing any discernible effect, exposure to high-energy visible light becomes selectively absorbed by molecules of the skin, leading to specific cutaneous changes.

Principles of Laser Generation Electrons surrounding an atom or molecule can exist at more than one energy level. In usual circumstances they are found at their lowest energy state or resting state (Fig. 2). If an electron absorbs the energy of a photon of light, it raises to a higher energy level ("excited" state). This "excited" but unstable electron can give up its energy by emitting a photon of light identical to the photon that was initially absorbed. This is called spontaneous emission. If a photon collides with another similarly "excited" electron, the

Curr Probl Dermatol, July/August i 9 9 8

electron will return to its resting state by emitting two photons that are synchronized in time and space and of same energy. This is called stimulated emission of radiation. The emitted photons may stimulate further emissions from excited atoms of the same type. Normally, the majority of electrons are in a resting state and stimulated emission is a rare event. To increase the likelihood of stimulated emission a higher proportion of excited electrons must be present, a state called "population inversion," When a population inversion occurs, the photons have a higher probability of encountering excited electrons and stimulating further emission of photons with the same energy. An external source of electrical chemical, or fight energy must be used to provide the source of excited "matter" a process called pumping.

Laser Construction A laser apparatus consists of three elements (Fig. 3). P u m p i n g System. The pumping system is the power supply or the external source of energy that creates a population inversion or "excited electrons" in the laser chamber (eg, high-powered flashlamp used in some dye lasers). Lasing M e d i u m , The lasing medium, the source of laser radiation, supplies the electrons needed for the stimulated emission of radiation. The medium has distinctive energy transitions that determine the wavelength of the emitted light; it can be gaseous (eg, argon, carbon dioxide, copper vapor, helium neon, krypton, excimer), liquid (eg, pulse dye), or solid (eg, ruby, Nd:YAG, alexandrite). Optical Cavity. The optical cavity is a chamber consisting of two parallel mirrors enclosing the laser medium, which is excited by the pumping system. Photons of energy in the axis of the chamber are reflected off the mirrors, stimulating further emissions in the same axis. The result of this chain reaction is the production of an enormous amount of light energy in a brief period. One of the mirrors is partially reflective, allowing some of the energy to leak from the chamber and form a laser beam.

Properties of Laser Light The produced laser light has several unique properties. Monoehromaeity. Laser light differs from sunlight or light emitted by a lamp in that it contains a single

133

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color or a very narrow band of wavelengths. The wavelength is solely determined by the medium present in the optical cavity. Monochromacity of laser light is very important because it allows for the selective absorption of the light by specific chromophores, such as melanin, or hemoglobin. Coherence. Laser waves are in phase both in space and time; in other words, they are spatially and temporally coherent. Collimation. As a result of spatial and time coherence, laser waves travel parallel to each other and have a low tendency for divergence. This highly ordered pattern of the light allows the beam to be propagated across long distances without beam spreading. High E n e r g y and Foeusability The coherence of a laser beam allows it to be directed to a small area with a very high intensity.

Laser-TimeDependence Laser light can be delivered as continuous, "quasicontinuous," or pulsed beams. The continuous lasers, such as carbon dioxide, argon, krypton, and argon dye lasers, emit a beam continuously at a constant energy. Quasicontinuous lasers, such as copper vapor, deliver a beam in which the pulses are so closely spaced that the tissue effect is similar to that of a continuous

134

beam. Pulsed lasers, such as the flashlamp-pumped pulsed dye laser, emit a beam in individual pulses with as long a period as the operator wishes between pulses. On the basis of their exposure duration, they are divided into long-pulsed (millisecond range) and short-pulsed lasers (nanosecond range). Q-switched lasers (Q-switched ruby, Q-switched alexandrite, Qswitched Nd:YAG) contain a photooptical switch or shutter within the laser cavity that allows the release of extremely short powerful bursts of high-energy light in the nanosecond domain (5 to 100 nsec). These lasers are used to target smaller structures, such as melanosomes and tattoo particles.

Radiometry Four simple definitions are needed to understand laser physics: energy, power, irradiance, and fluence. Energy. Energy is the capacity to do work; it is measured in joules. Power. Power is the rate at which energy is delivered; it is measured in watts. By definition, one watt equals one joule per second. Irradiance. Irradiance, or power density, is the rate of energy delivery per amount of skin surface during a single pulse (in watts per square centimeter). In other words, it describes the intensity of energy delivery.

Curr Probl Dermatol, July/August 1998

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The shorter the pulse duration of a laser, the higher the irradiance must be to deliver a sufficient amount of energy for clinical effect. Flnenee. Fluence (or energy density) is defined as the amount of energy delivered per amount of skin surface. It describes the density or brightness of laser light on the skin and it is measured in joules per square centimeter. The energy density is inversely proportional to the radius (r) of the spot size, defined as the area of the skin over which the laser beam is spread (Energy density = ~r2). For

Curr Probl Dermatol, July/August 1998

instance, when a port-wine stain is treated with a pulsed-dye laser at 3 joules per pulse and a spot size of 10 ram, the estimated energy density is approximately 4 J/cm 2. When the same light source at the same energy level is focused to a spot size of 5 mm, the calculated energy density is around 16 J/cm 2. Therefore halving the spot size increases the energy density by a factor of 4. Conversely, to achieve the same energy density with a spot size one half the diameter, the laser energy output would have to be reduced by a factor of 4.

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Other important laser parameters are those of laser exposure duration (called pulse width or pulse duration for pulsed lasers) and the profile of a laser beam. The laser exposure duration sets the time over which the energy is delivered. Most lasers in dermatology use exposure times ranging from nanoseconds to milliseconds. Tissue effects also depend on the type of beam. The ideal laser beam has a uniform distribution of energy across the whole area of the beam (top-hat distribution), whereas many lasers produce gaussian beams with more energy in the center than at the margins, which gives a n o n u n i f o r m tissue effect. This explains why the purpura produced by the pulseddye laser is not uniform across the tissue treated.

Skin Optics When a laser beam strikes the skin, there are four possible interactions that can occur: reflection, scattering, transmission, or absorption of light (Fig. 4). According to the first law of photobiology, a tissue effect occurs only when light is absorbed. Reflected or transmitted light has no tissue effect. 11 When light absorption occurs, the photon surrenders its energy to a chromophore, defined as an atom or a group of atoms that impart a color to a substance and absorbs at a specific wavelength. The chromophore becomes excited and undergoes a photochemical reaction or dissipates the energy as either heat or reemission of light. In most clinical settings the absorbed energy is converted to thermal energy with heating of the chromophore and destruction of the absorbing tissue. Laser light of a specific wavelength can thus be absorbed selectively by a cutaneous chromophore to produce the desired tissue effect. The skin contains distinct pigments and microscopic structures with different absorption spectrum. 11 The absorption spectrum of the chromophore molecules at typical concentrations in the skin is depicted in Fig. 5. Optical penetration in the skin is affected by two essential processes: absorption and scattering of light. In the epidermis absorption is the dominant process over most of the optical spectra, whereas in the collagen-rich dermis optical penetration is largely dominated by scattering. 12 At wavelengths above 1300 nm light penetration is shallow because of light absorption by water, the dominant chromophore at this end of the spectrum, which absorbs most of the light. On the

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other end of the spectrum, ultraviolet wavelengths (290 to 400 nm) are strongly absorbed mostly by epidermal elements such as melanin, proteins, deoxyribonucleic acid (DNA), and urocanic acid. Over the visible spectrum of EMR, the depth of penetration in the skin is inversely related to wavelength: the longer wavelengths penetrate deeper. 13 The most penetrating wavelengths are in the red and near-infrared spectrum (600 to 1200 nm). This range has been termed as an optic window for selective targeting of individual chromophores. The example of hemoglobin illustrates the difficulties in tailoring a wavelength to a specific chromophore. Hemoglobin has its peak of absorption in the blue band (418 nm). However, light penetration is limited at this wavelength and longer wavelengths near the 577 nm absorption peak are chosen to treat vascular lesions. Fig. 6 shows the approximate optical penetration depths and corresponding wavelengths of different lasers of current interest in dermatology.

Laser-Tissue Interaction The effect of lasers on tissue are separated into thermal and mechanical effects. T h e r m a l Effects. Laser light can lead to a tissue effect when it is absorbed and converted to energy, mostly heat. This biologic effect is determined by the temperature achieved within the tissue. 14 Increases of temperature of only 5 to 10 ° C can cause cell injury and subsequent inflammation and repair. At temperatures below 100 ° C macromolecules, proteins and DNA molecules, become denatured. At temperatures above 100 ° C intracellular water exceeds its boiling point, leading to vaporization of tissue. The steam produced causes a rapid increase in pressure that damages cellular elements and blood vessels. Further heating results in desiccation and charring. To determine the tissue effect by lasers, heat conduction must be taken in consideration. When light is absorbed by a target, heat loss occurs immediately by conduction to adjacent tissues, a process called thermal relaxation. The speed of thermal relaxation is expressed by the thermal relaxation time, which is defined as the time necessary for the targeted tissue to cool down to half the temperature to which it has been heated. The thermal relaxation time varies according to the size of the targeted structure. Small objects cool faster than large ones. For instance, melanosomes of 0.5 to 1 pm have a short thermal relaxation time (less than 1 psec)

Curr Probl Dermatol, July/August 1998

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compared with blood capillaries with a diameter of 10 to 100 gm, which have a thermal relaxation time within the millisecond range (1 to 10 msec). The tissue effect of lasers is primarily affected by

Curr Probl Dermatol, July/August 1998

two parameters: the heating of chromophores and the secondary spread of heat to the adjacent tissues• The degree of thermal damage is influenced first by the height of temperature reached within the target

137

Stratum corneum Epidermis

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FI6.6. Approximate optical penetration depth for different laser systems (wavelength in nanometers). CO2, Carbon dioxide; LPDL, long-pulse dye; Alex, alexandrite.

and second by the length of time that the target remains heated. The extent of tissue damage is affected by the energy density, the pulse duration, and the heat conduction. Mechanical Effects. When the pulse duration is less than the thermal relaxation time, there is a sudden thermoelastic expansion resulting from spatially localized heating--a kind of tissue microexplosion. This sudden change generates acoustic waves that damage the absorbing tissue. Photoacoustic or photomechanical damage has been documented in the treatment of vascular and pigmented lesions. When treating vessels with a long-pulse (1.5 msec) dye laser, the estimated rate of temperature rise in erythrocytes is 1070 C per second. 15 This rapid temperature rise may be responsible for generating pressure waves that lead to rupture of the vessel and to purpura. Likewise, in the treatment of pigmented lesions with Q-switched lasers, the targeted pigment within melanosomes is heated abruptly, resulting in

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rupture of the melanosomes and mechanical damage to the nuclei of melanocytes.16

Selective Photothermolysis In absorbing targets, light energy is converted to heat, which then dissipates through conduction and radiation transfer and leads to passive cooling. The competition between active heating and passive cooling determines how high the temperature reaches within the target. The most selective thermal damage or selective photothermolysis occurs when the energy is deposited at a rate faster than the rate of cooling of the targeted structures, or, in other words, when the heating time approaches the thermal relaxation time of the target. If the pulse duration of the emitted wavelength is longer than the thermal relaxation time, heat diffuses from the target before the latter is irreversibly thermally damaged. If, however, the laser exposure duration is just less than the thermal relaxation time, the target can not get rid of its heat during laser exposure

Curr Probl Dermatol, July/August 1998

and irreversible thermal damage is confined within the target. To achieve selective photothermolysis requires (1) a wavelength at which the desired target preferentially absorbs, (2) an exposure duration of less than the thermal relaxation time of the target, and (3) energy fluences high enough to reach a damaging temperature within the targeted structure. The thermal relaxation time of a given structure is proportional to the square of size. Thus a 0.5 g m melanosome should cool in 25 x 10.8 seconds, or 250 nanoseconds, whereas a 0.1 mm port-wine vessel should cool in 10.2 seconds, or 10 milliseconds. Even greater variation in thermal relaxation time is expected given the natural variation of target sizes in tissue. The dimensions of the target are therefore important in determining the thermal relaxation time and in optimizing the parameters of laser exposure duration or pulse duration. Examples of targets in skin that can be selectively damaged by the process of selective photothermolysis include blood vessels and pigment. Thermal damage can be confined to a blood vessel with limited collateral destruction by choosing a wavelength absorbed by hemoglobin, such as 585 rim, and a laser pulse duration shorter than 1 to 10 milliseconds, which is the thermal relaxation time of blood vessels with diameters of 10 to 100 gin. The flashlamp-pumped pulsed dye laser was the first laser developed on the basis of the theory of selective photothermolysis and the first laser designed and built for medical use. It was initially designed to emit at 577 nm, the last peak in the absorption peak of oxyhemoglobin, and was then converted to 585 nm to increase penetration of the laser light. With a pulse duration of 450 gsec there is sufficient energy absorption by hemoglobin to cause blood vessel coagulation. 17 Too short a pulse duration (1 gsec) causes microvascular rupture and hemorrhage, 18 whereas a long exposure time increases the risk of damage to the surrounding tissue with unacceptable perivascular damage. 19 Another example implementing the theory of selective photothermolysis is the treatment of pigmented lesions. Melanosomes are the fundamental site of melanin synthesis within melanocytes and occur in the form of 0.5 to 1 gm intracytoplasmic organelles. Their thermal relaxation time has been estimated to range from 250 to 1000 nsec. n With use of wavelengths absorbed by melanin, such as 694 nm (Q-switched ruby) or 755 nm (Q-switched alexandrite), with a laser pulse duration shorter than the thermal relaxation time of melanosomes (<1 gsec), selective targeting of melanosomes can be

Curr Probl Dermatol, July/August 1998

achieved. A similar mechanism is observed in the treatment of tattoos, which consist of intracellular, submicrometer-sized, insoluble ink particles contained in phagocytic cells. Lately laser skin resurfacing and laser-assisted hair removal have been used in the clinical arena on the basis of the principles of selective photothermolysis and are discussed below in more detail.

Laser Safety Laser hazards are divided in two categories: beam hazards, which are related to direct or incidental impact, and nonbeam hazards. Beam hazards, such as fire, thermal burns, and ocular damage occur whenever the laser is activated. Flammability accidents occur when the laser is used in the presence of oxygen (ie, ignition potential of the 585 nm pulsed dye laser during anesthesia). 2° Flammable items such as drapes, towels, or sponges can be ignited by a direct or reflected laser beam. To avoid this risk, wet or nonflammable material should be placed in the surgical field and all excess draping should be removed from the site. Surgical instruments with a bright reflective surface should be either ebonized or covered with wet sponges to prevent inadvertent irradiation. Alcohol is extremely hazardous when exposed to the intense heat generated by the lasers. Thus solutions containing alcohol, such as Hibiclens, may easily ignite and should be avoided in the laser impact site. Exposure to the solvents and organic dyes in dye laser systems is also potentially hazardous. Ocular risks are the most serious encountered in laser use. The eye may be exposed directly in the laser beam's path or indirectly by a reflected beam. Each wavelength interacts differently with tissue and therefore can produce different types of ocular damage. Carbon dioxide laser radiation (10,600 nm) is absorbed by water. When light of this wavelength irradiates the eye, it is absorbed by the cornea, leading to extensive corneal damage. Laser light in the visible (400 to 780 nm) and near-infrared (780 to 1400 nm) portions of the electromagnetic spectrum are transmitted through the transparent cornea and lens and are focused on a retinal spot of 10 to 20 gm resulting in a retinal burn and visual damage. To protect the eyes from laser damage, adequate wraparound glasses must be worn by all present in the laser room.

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There are many manufacturers who produce goggles in several designs for use with any of the lasers. Nonbeam hazards include plume hazards and are currently the subject of widespread concern. Research has shown that harmful particulates such as intact virions and viral DNA are present in the plume during carbon dioxide laser radiation. Intact human papillomavirus DNA has been found in carbon dioxide laser vapor. 21 Transmission and infection by hepatitis B and human immunodeficiency virus viruses through laser plume or smoke represent a serious potential hazard. Molecular studies have detected human immunodeficiency virus and simian immunodeficiency virus DNA in laser smoke from irradiation of infected cultured cells by a continuous carbon dioxide laser. 22,23 However, their infectivity is unknown because both viruses appeared to be damaged by the laser. More concern exists regarding the aerolization of tissue particles during the microexplosions of tissue treated by ultrashort pulses, such as the Q-switched ruby or the Q-switched Nd:YAG. The debris contains viable cells, microorganisms, and blood. The velocity of microexplosion and the spread of tissue fragments exceeds the speed of sound and may escape collection by smoke evacuators. This problem has been addressed by some manufacturers with the use of a splatter shield for the laser handpiece. However, additional protective measures, such as the use of gloves

140

and gowns, should be implemented during treatment with Q-switched lasers. Lasers are high-voltage electrical devices and carry a risk of inadvertent discharge. Today most laser systems used have safety controls built in them that shield the operator and the patient from high voltage, minimizing the possibility of electrical accidents. Other appropriate safety precautions during laser surgery include the use of proper gloves and gowns by all personnel throughout all procedures. The wearing of properly filtered and tied laser masks can greatly reduce the respiratory exposure to viral and other infectious agents. Wavelength-specific wraparound eyeglasses are mandatory. Laser surgery should be presumed to contain liberated viable infectious particles in the plume of smoke. The risk of infection in laser operators can be minimized through the use of a high-efficiency smoke filtration system.

Lasers for Vascular Lesions Laser treatment of congenital and acquired vascular lesions has progressed significantly over the past few decades. Continuous-wave lasers were the first to be applied for the treatment of these lesions, but their use was often complicated by unacceptable textural changes of the skin. The development of pulsed lasers has redefined the therapy of vascular disorders.

Curr Probl Dermatol, July/August 1998

Types of Lasers Continuous and Quasicontinuous Wave Lasers

Argon Laser. The argon laser is a continuous wave laser that emits in the blue-green portion of the electromagnetic spectrum, with peak emissions at 488 and 514 nm (Fig. 7). Argon light is absorbed by both oxyhemoglobin and melanin and can penetrate approximately 1 mm into the skin. From the 1970s until the mid to late 1980s this laser was the treatment of choice for many vascular lesions. Despite selective absorption of argon laser light by hemoglobin in blood vessels, the continuous nature of the beam produces nonspecific thermal injury in the tissue adjacent to vascular targets. 5 In addition, significant absorption by melanin results in pigmentary changes, such as hyperpigmentation and, occasionally, permanent hypopigmentation. Histologic examination of argontreated port-wine stains demonstrates the nonselective damage induced by the laser with diffuse coagulative necrosis of the epidermis and papillary dermis, followed by microscopic fibrosis and scarring in the healing phase. 19 One of the first clinical applications of the argon laser was in the treatment of port-wine stains. The treatment resulted in good fading of the lesions but was associated with skin texture changes in 5% to 38% of the patients and permanent pigmentation in more than 20% of treated patients (Fig. 8). 24,25 The high risk of side effects in the treatment of port-wine stains and the development of the pulsed dye laser have left little place for the use of the argon laser in the treatment of all except thick, nodular port-wine stains. 26 It is, however, effective in treating facial telangiectasia, 27 highflow spider angiomas, 2s pyogenic granulomas, and thick venous lakes. 6 Argon-Pumped Tunable Dye Laser. The argonpumped tunable dye laser consists of an argon laser as the power source and a solution of a variety of organic dyes as the active medium. It produces a narrow band of light at wavelengths ranging from 488 to 638 nm. The continuous laser beam can be mechanically shuttered, but truly pulsed laser light cannot be produced. When rhodamine 6G is used as the dye, the laser produces 577 nm wavelength light that can be tuned up or down 20 nm with use of a computer-controlled prism. (The argon laser can also be uncoupled from the dye laser.) The continuous-wave tunable dye laser can be used in this way to treat a variety of vascular lesions, such as port-wine stains, 29 facial telangiectasia, and

Curr Probl Dermatol, July/August 1998

Fill. 8. Scarring after treatment of port-wine stain on neck with the argon laser.

spider angiomas. 3° There are no studies comparing the efficacy of the continuous-wave tunable dye laser with the argon laser. Although the former should theoretically produce slightly better results in the treatment of vascular lesions because of better absorption of hemoglobin at 577 nm, the difference may not be clinically relevant. At 630 nm the argon tunable dye laser produces a red light that is used as a source for photodynamic therapy, a form of therapy for various cutaneous and noncutaneous tumors. 31 Copper Vapor Laser. The copper vapor laser is a quasicontinuous wave laser that emits a yellow light beam at 578 nm and a green beam at 511 nm. The yellow beam is well absorbed by oxyhemoglobin and is

141

TABLE 1. Commonly used lasers and light sources for vascular cutaneous lesions Laser/light source

Pulsed PDL

Wavelength (nm)

585

450 gsec 300-500 msec 1.5 msec 1.5 msec 1.5 msec 450 gsec, 1.5 msec

511,578

Copper Vapor (Continuum Biomedical)

20 nsec (gated)

532

Aura Starpulse (Laserscope)

1-50 msec

CB Diode/532 (Continuum Biomedical) DioLite 532 (Iriderm) VersaPulse (Coherent)

1-100 msec 2-10 msec 2-10 msec

Coherent Innova (Coherent) Digital Spectrum K1 (hgm) PhotoDerm VL (ESC)

0.01-5.0 sec 0,02, 0.05, 1, 2, 5, 10 sec 2-25 msec

590,595,600

Selectable pulsed dye

585,590,595,600

KTP (frequency-double Nd:YAG)

Continuous wave Argon-pumped tunable dye Krypton Intense pulsed light source

488,514,577-630 520,531,570 515-1200

used in the treatment of vascular lesions, whereas the 511 nm green beam is used to treat superficial pigmented lesions. The copper vapor delivers a train of short 20 nanosecond pulses with a 2 mJ power per pulse and a repetition rate of 10,000 to 15,000 pulses per second (10 to 15 kHz). The duration of 20 nanoseconds is approximately 22,500 times shorter than that of the pulsed dye laser (450 gsec). Because of the short interval between pulses (67 to 125 gsec), the vessels do not cool adequately after laser pulsing and the vascular injury produced is identical to that of a continuous wave laser. Copper lasers are used to treat port-wine stains, particularly nodular typesY larger telangiectasia, 33 venous malformations, 34 angiokeratomas, and pyogenic granulomas. 35 Side effects of this laser include posttreatment hypopigmentation, which is usually transient, and hypertrophic scarring. 35 Potassium Titanyl Phosphate Laser. The potassium titanyl phosphate (KTP) laser uses Nd:YAG crystal (1064 nm) that is frequency-doubled with a KTP cricstal to produce a green light at 532 nm. KTP lasers were originally only continuous-wave lasers and were used in the treatment of facial telangiectasia 36 but have been superseded by the recently developed 1 to 100 millisecond pulsed KTP sources (see Pulsed Lasers). Krypton Laser. The krypton laser is a continuouswave source that emits yellow light at 568 nm and two bands of green light at 521 and 530 nm. The shorter

142

Pulse duration

Vascular lesion STL-lb (Candela) PhotoGenica V (Cynosure) ScieroLASER (Candela) PhotoGenica LV (Cynosure) ScleroPLUS (Candela) Cynosure VLS (Cynosure)

Long-pulse dye

Quasicontinuous wave Copper vapor

System name

green light wavelengths can be used to treat pigmented epidermal lesions or can be filtered out, leaving just the yellow wavelengths (568 nm) for the treatment of superficial vascular lesions. 37 Continuous-Wave Lasers With Robotized Optical Scanners. To optimize treatment and limit nonspecific tissue injury with the use of continuous- and quasicontinuous-wave lasers, automated scanning handpieces can be attached to deliver small, nonadjacent spots in a predetermined treatment area. One such automated handpiece, the Hexascan (Prein & Partners, Ferney-Voltaire, France) rapidly delivers numerous 1 m m circular spots with 50-millisecond intervals that fill up a larger hexagonal-shaped treatment area of 1 to 13 m m adjustable diameter. 38 Scanners were developed to increase the safety margin and reproducibility of continuous-wave visible laser sources and, although they have been successful in this challenge, the pulse duration remains too long for selective photothermolysis to be achieved, thus increasing the risk of extensive thermal damage. 29 Pulsed Lasers Pulsed Dye Laser. The flashlamp-pumped pulsed dye laser (PDL) was the first laser developed based on the theory of selective photothermolysis ~° and was designed specifically to treat vascular lesions. It uses a high-power flashlamp to energize an organic dye (rhodamine) and produce a true pulse of yellow light. The original PDL emitted at a wavelength of 577 nm, coin-

Curr Probl Dermatol, July/August 1998

Spot size (ram) 2,3,5,7 3,5,7,10 2 x 7 (elliptical) 3, 5, 7, 1 0 m m ; 2 x 7 m m 2,3, 5, 7, 1 0 m m ; 2 x 7 m m 3, 5, 7, 1 0 m m ; 3 x 5 m m

Other features and characteristics

Dynamic cooling

4 0 0 , 8 0 0 , 1 2 0 0 gm 200, 500,700, 1000, 1400 gm 1-10 mm

Can be used with scanner (Hexascan) Can be used with scanner (Smartscan) Diode pumped Diode pumped Operated with chill tip

50, 100, 200, 500, 1000, 2000 gm 100 gm; 1, 2 mm 8x35mm;8x15mm

Cooling gel

0.5,1,24mm

ciding with the last absorption peak of oxyhemoglobin. 39 The dye was then modified to produce light at 585 nm and to allow for deeper tissue penetration of the light, despite a slightly less selective vascular injury. 4° The pulse duration of the traditional PDL (450 gsec) is shorter than the calculated thermal relaxation time of cutaneous vasculature (1 to 10 msec for vessel diameter of 10 and 100 gm, respectively) and allows for sufficient energy absorption by oxyhemoglobin to cause red blood cell coagulation. 41 Histologic examination of port-wine stains after treatment with PDL demonstrate an intact epidermis and superficial dermal blood vessels containing agglutinated erythrocytes, fibrin, and thrombi. 42 These histologic findings correlate with the purpura seen clinically immediately after exposure to PDL. One month after treatment the destroyed ectatic vessels are replaced by normal-appearing vessels without evidence of dermal scarring. 43 Individual laser pulses are emitted through a fiberoptic handpiece and can be delivered at a repetitive rate of up to 1 Hz with spot sizes ranging from 2 to 10 mm. The pulses are placed adjacent to one another with approximately 18% overlap to avoid missing areas in between the circular spots, thus preventing a reticular or honey-combed appearance of the treated site. 44 The energy density of the PDL can be varied ranging from 5 to 10 J/cm 2. In general, lower fluences are used for the treatment of macular disorders and

Curr Probl Dermatol, July/August 1998

higher fluences are used in more hypertrophic vascular lesions. The PDL is considered to be the treatment of choice for many vascular lesions, such as port-wine stains, particularly in young infants and children, 45 facial telangiectasia including spider angiomas and telangiectatic erythema associated with rosacea, 46 superficial hemangiomas, 47 and poikiloderma of Civatte. 48 Treatment with PDL has been also used successfully to treat hypertrophic scars,49warts, 50 and striae distensae. 51 Treatment with the pulse dye laser is relatively well tolerated by adults and only occasionally requires anesthesia. In infants and children treatment is often traumatic and requires topical, local, regional, or even general anesthesia in certain cases. 52 Discomfort during laser treatment is described as a rubber band snapped against the skin. Treatment of more sensitive areas, such as the infranasal and periorbital skin, digits, and anogenital area, can be best performed with the use of a topical or local anesthetic. Immediately after treatment the treated areas develop purpura, which gradually resolves in approximately 7 to 14 days. Side effects of the PDL in the treatment of port-wine stains include atrophic scarring (0.1% of patients), 53 usually as a result of excessive energy delivery, hypopigmentation (2.6%), 54 and, rarely, hypertrophic scarring. Long-Pulse Dye Lasers. The optimal pulse duration for treatment of vessels 30 to 150 g m in diameter, typically found in port-wine stains, lies in the 1 to 10 millisecond domain. 15 Recently, slightly longer pulse dye lasers (Sclerolaser/ScleroPLUS, Candela Laser Corporation, Wayland, Mass., and LV, Cynosure, Chelmsford, Mass.) have been developed with pulse widths of 1.5 milliseconds, which is three times the pulse duration of the traditional pulsed dye laser. Their wavelength has been also modified to emit at 585, 590, 595, or 600 nm in an effort to increase the depth of penetration (Table 1). The longer pulse duration more closely approximates the thermal relaxation time of vessels in port-wine stains and in a variety of acquired cutaneous vascular lesions, whereas the deeper penetration of light may allow for the effective treatment of thicker or deeper vascular lesions (ie, hypertrophic port-wine stains and facial telangiectasia). Early experience has demonstrated that the longpulse dye lasers may be more effective than the traditional 450 microsecond PDL in clearing port-wine stains with fewer treatment sessions needed. Facial

143

vessels that have not been responsive to PDL treatmerit, as well as the blue, deeper vessels in the paranasal folds, have shown significant response after treatment with the long-pulse dye lasers. Results in the treatment of leg veins have also been encouraging.54 Frequency-doubled Q-switched Nd: YAG lasers. As mentioned above, long-pulse frequency-doubled Qswitched Nd:YAG lasers that emit green light at 532 nm have recently been developed in an effort to treat vascular anomalies without purpura in the postoperative period, a finding invariably seen after treatment with the pulsed dye laser. Several 532 nm long-pulse lasers are now approved for dermatologic use (Aura, Laserscope-Orion, San Jose, Calif.; VersaPulse, Coherent Laser Co., Palo Alto, Calif.; CB Diode/532, Continuum Biomedical, Dublin, Calif.; Diolite 532, Iriderm, Mountain View, Calif.). Each produces pulses of 532 nm light in pulse durations ranging from 1 to as long as 100 milliseconds delivered to tissue by a fiberoptic handpiece. Preliminary results have shown these lasers to be effective in the treatment of facial telangiectasia and a variety of vascular anomalies, including spider angiomas. Work is still in progress to determine their efficacy in the treatment of port-wine stains and leg telangiectasia. The distinct advantage of this group of lasers is the absence of purpura in the postoperative period. This results from the slow heating of blood vessels at longer pulse durations, allowing for cooling of the vessels without rupture of the vessel wall or red blood cell extravasation into the interstitial space. The disadvantage of the 532 nm pulsed sources is their short wavelength, which limits their depth of penetration in the skin and which competes with epidermal melanin more than the longer wavelengths, resulting in potential pigmentary changes. Pulsed Light Sources. The PhotoDerm VL/PL (ESC Medical Systems, Needham, Mass.) is a laserlike device that uses a flashlamp to produce a spectrum of intense pulsed broad-band light emitting from 515 to 1200 nm. The PhotoDerm produces noncoherent, pulsed light at variable pulse durations and intervals. A series of cutoff filters is used to shift the short end of the spectrum in increments ranging from 515 to 590 nm to treat vascular lesions. The device generates a variety of fluences (up to 80 J/cm 2) in single-, double, or triple-pulse modes in the 2 to 10 millisecond domain. The light is delivered by a fiber to an 8 x 35 mm aperture allowing treatment of large areas. In an effort to decrease epidermal damage and to increase

144

the efficiency of light energy to deeper vessels, a coupling gel is applied on the skin. Advantages of this device are its versatility given the wide range of wavelengths and pulse durations that allow treatment of deeper vascular lesions and the absence of purpura after treatment. Disadvantages of PhotoDerm VL compared with the pulsed dye laser are the longer treatment time, the increased number of treatment sessions required to clear vascular lesions, and the degree of experience needed by the laser operator to achieve excellent results. The PhotoDerm has been shown to be effective in the treatment of facial telangiectasia, leg telangiectasia, hemangiomas, and port-wine stains.55,56

Clinical Applications Port-Wine Stains. Port-wine stains are capillary vascular malformations occurring in 0.3% to 0.5% of newborns. 57 They are composed of ectatic vessels in the papillary dermis. The lesions become progressively ectatic and, in 65% of patients, they develop hypertrophy or nodularity by the fifth decade of life. 58 Various treatment options have been applied for the treatment of port-wine stains, including cryotherapy, excision, and radiation therapy. 59 The advent of laser technology and its applications on the basis of the theory of selective photothermolysis led to a more effective treatment of port-wine stains. The pulsed dye laser is currently the treatment of choice for these lesions, especially in children (Table 2). Macular and mildly hypertrophic port-wine stains are best treated with the pulsed dye laser (450 gsec), which can produce remarkable clinical lightening with only a few unfavorable side effects (Figure 9). 45 More advanced nodular or hypertrophic forms may not respond to the pulsed dye laser and are best treated with the long-pulse dye lasers (1.5 msec), the quasicontinuous and continuous mode lasers, or the broad-band light source (PhotoDerm VL). Multiple treatment sessions are required to clear portwine stains, and, in spite of a variable incidence of lightening after pulsed dye laser treatment, complete resolution of the lesions can be achieved with repetitive laser treatments in the majority of patients. 6° Studies have revealed that approximately 75% of patients with port-wine stain have at least 50% lightening of lesions after a total of four treatments. 61 The rate of clearing of port-wine stains largely depends on their anatomic location, with the distal extremities and truncal lesions responding less favorable than lesions

Curr Probl Dermatol, July/August 1998

FIG. 9, Port-wine stain treated with pulsed dye laser. A, Before treatment. B, Immediately after treatment, demonstrating

purpura that worsens for 24 hours and then lightens over 7 to 14 days. C, After four laser treatments, showing almost complete port-wine stain lightening.

Curr Probl Dermatol, July/August 1998

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TABLE 2. Response of vascular lesions to different types of lasers

Port-wine stain Type of laser or light source Pulse dye (585 nm) Long-pulse dye (590,595, 600 nm) Continuous wave (argon, tunable dye) Pulsed KTP (532 nm) Copper vapor (578 nm) Intense pulsed light source (515-590 nm)

Hemangiomas

Face

Legs, in conjunction with sclerotherapy

Macular

Hypertrophic

Superficial

Deep

Spider angiomas

Excellent Excellent

Poor Excellent

Excellent Excellent

Poor Poor

Excellent Excellent

Excellent Excellent

Poor Fair

Fair

Good

Fair

Poor

Good

Fair

Poor

Good Good Good

Excellent Good Fair

Fair Fair Good

Poor Poor Poor

Good Good Good

Excellent Good Excellent

Good Fair Good

on the head and neck. Treatment response also varies in port-wine stains of the head and neck, with midline port-wine stains clearing faster than lesions over the second branch of the trigeminal nerve. 62 In general, laser treatment of port-wine stains should be initiated as soon as possible during infancy to decrease the psychologic impact of the birthmark. The use of the longpulse dye lasers (1.5 msec) has shown encouraging results in the treatment of port-wine stains, with faster clearing of lesions and fewer treatment sessions. As our experience with this device increases, it may become the laser of choice for all port-wine stains. Hemangiomas. Capillary hemangiomas are the most commonly described vascular tumors. They are frequently located on the head or neck and occur either at birth or shortly thereafter. 63 During the first year of life they undergo rapid proliferation and growth, followed by complete or partial involution by age 12 years.64 Although hemangiomas involute spontaneously, they frequently leave residual fibrofatty tissue and atrophic skin. Furthermore, larger hemangiomas may interfere with vital structures. In the past treatment modalities have included cryotherapy, sclerotherapy, and radiation therapy, all of which resulted in significant scarring. Systemic steroids and interferon alfa-2a have been used successfully during the proliferative phase of hemangiomas because of their inhibitory effect on angiogenesis; however, their side effect profile poses certain limitations in clinical use. 65,66 The pulsed dye laser has significantly improved our ability to treat capillary hemangiomas, which are composed mostly of superficial vessels (Figure 10). 67 Multiple treatments, however, may be needed to achieve maximal clearing. Early initiation of treatment is also advocated to minimize rapid enlargement of the tumor,

146

Telangiectasia

bleeding, ulceration, or obstruction of vital organs. Recommended treatment intervals are 2 to 3 weeks for proliferating hemangiomas and 1 to 2 months for involuting hemangiomas. Because of its limited skin penetration, the pulsed dye laser is not effective in treatment of the deep component of superficial hemangiomas or in cavernous (deep) hemangiomas.68 The latter are more likely to respond to treatment with the nonselective continuous-wave Nd:YAG laser, which penetrates deeper but has an increased risk of textural abnormalities. 8 Studies are underway to determine the efficacy of the long-pulse (1.5 msec) dye lasers and pulsed light sources in the treatment of hemangiomas. Telangiectasia. Telangiectasia can be classified into four types: linear, arborizing, spider, and punctiform or papular. 69 Red linear and arborizing telangiectasia frequently occur on the face, particularly on the nose, cheeks, and chin. They measure 0.1 to 1.0 mm in diameter and probably result from a variety of factors, such as genetic predisposition, hormonal factors, and physical stress. Chronic sun exposure, emotional states, alcohol intake, pregnancy, and estrogen ingestion have been causally related to the development of telangiectasia. 69 Two approaches have been developed for the treatment of telangiectasia with lasers, based on the existing laser devices: the pulsed dye laser (including the more recent long-pulse dye laser), which leaves purpura after treatment, and the long-pulse frequencydoubled Nd:YAG laser sources (532 nm), which do not cause any purpura. The pulsed dye laser has been shown to effectively treat facial telangiectasia as well as rosacea-associated telangiectasia and erythema, spider angiomas, telangiectasia associated with CREST (calcinosis, Raynaud's phenomenon, esophageal involvement, sclerodactyly, and telangiectasia) syndrome, and gener-

Curr Probl Dermatol, July/August 1998

alized essential telangiectasia (Figure 11). In a large series of patients in which the regular PDL was used, 97.5% of the patients achieved a good to excellent response in the treatment of linear and spider facial telangiectasia with fluences of 6.0 to 7.5 J/cm 2 and a 5 mm spot size. 7° Pigmentary changes occurred in 3% of patients and resolved in 12 months. Larger linear facial telangiectasia can be effectively treated with PDL and an elliptical spot size of 2 x 7 mm. The long-pulse dye laser is effective for all the above types of telangiectasia as well as the larger linear telangiectasia of the paranasal folds, which may be resistant to treatment with PDL. The new long-pulse frequency-doubled Nd:YAG lasers (Aura, Laserscope-Orion, San Jose, Calif.; VersaPulse, Coherent Laser Co., Palo Alto, Calif.; CB Diode/532, Continuum Biomedical, Dublin, Calif.; Diolite 532, Iriderm, Mountain View, Calif.) have been also used successfully in the treatment of facial telangiectasia and do not result in any purpura postoperatively. Other advantages include the abbreviated wound healing phase with limited crusting and the acceptability by patients. These lasers are also advantageous in patients with telangiectasia and background erythema who desire treatment of the tetangiectasia only. Disadvantages include the fact that treatment is tedious and time consuming, requiring several treatment sessions in patients with extensive telangiectasia. Other laser systems used are the argon-pumped tunable dye laser, the argon laser, and the quasicontinuous mode lasers (copper vapor, copper bromide, krypton, KTP). The pulsed light source (Photoderm VL) is also highly effective in clearing facial telangiectasia in several treatment sessions without the development of significant purpura. The traditionally used continuous-wave visible laser sources are also effective in treating facial telangiectasia without postoperative purpura, but the rate of clearing is lower than with the pulsed sources and the risk/benefit ratio is slightly higher. Several approaches that use laser light sources have been developed for the therapy of leg telangiectasia. Currently, sclerotherapy continues to be the treatment of choice for leg veins, with various laser and light sources being used as an adjuvant treatment for the achievement of better vessel clearance. The pulsed dye laser at 585 nm may be effective in leg veins less than 0.2 mm in diameter but does not work well for largercaliber vessels. 71 In one study there was persistent hypopigmentation and hyperpigmentation in almost

Curr Probl Dermatol, July/August 1998

FIG. 10. Hemangioma in child treated with PDL. A, Before laser treatment. B, After several laser treatments. (Courtesy of Jerome Garden, MD.)

50% of patients after PDL treatment. 72 The long-pulse dye laser (1.5 msec) has been used at wavelengths of 595 and 600 nm with clearance of leg telangiectasia and infrequent complications. In a recent study of patients with leg veins, fluences of 15 to 20 J/cm 2 were used for up to three treatments, with significant clearing of the treated vessels. 73 A similar leg vein study using a 595 nm long-pulse dye laser at fluences of 15 to 18 J/cm 2 showed more than 50% clearance of vessels in 53% of cases with minor side effects.54 After treatment, purpura was produced for approximately 7 to 15 days and was sometimes followed by transient hyperpigmentation. The pulsed light source PhotoDerm has been used for the treatment of leg veins with sizes ranging from 0.3 to 1 ram. In one study treatments consisted of a sequence of pulses at fluences ranging from 25 to 70 J/cm 2 and at cutoff wavelengths of 515, 550, 570, or 590 nm, depending on the diameter of the vessel. 55 The authors showed over 50% clearing of vessels in 94% of cases after one to five treatments at 2- to 4-

147

FIG. 11. Facial telangiectasia treated with PDL. A, Before treatment. B, After two treatments with PDL. Patient had third treatment with PDL to complete treatment process. Purple dots were marked to delineate areas for third treatment.

week intervals. The risk of scarring and hyperpigmentation was found to be lower than for other treatments.

Lasers for Pigmented Lesions Skin pigmentation results from the deposition of chromophores in the epidermis or dermis. These chromophores include both endogenous compounds such as melanin, as well as exogenous material such as traumatic and cosmetic tattoos. Skin pigmentation is the result of the size, number, and distribution of melanosomes within melanocytes and keratinocytes. Dermal pigmentation may result from an arrest of dermal melanocyte migration during embryogenesis, resulting in dermal melanocytoses such as nevus of Ota. As well, injury to the epidermal basal layer may result in pigmentary incontinence, leading to postinflammatory hyperpigmentation. The fundamental principle behind laser treatment of cutaneous p i g m e n t a t i o n is selective destruction of undesired pigment with minimal

148

collateral damage. 1° This destruction is achieved by the delivery of high energy at the absorptive wavelength of the selected chromophore. For example, lasers used to treat melanocytic lesions take advantage of the broad absorption spectrum of melanin. The idea of treating cutaneous pigmented lesions with lasers was first tested by Goldman et al 74-76 in the early 1960s with use of a normal mode ruby laser. These studies suggested that the target was the m e l a n o s o m e . Subsequent studies identified the melanosome as the target of destruction with the excimer laser, 77 the Q-switched ruby laser, 16,7s the pulsed dye laser, 79 and the Q-switched Nd:YAG laser, s° Electron microscopic evaluation has demonstrated that melanosome destruction is the first subcellular event after irradiation with these short-pulsed lasers. Subsequent leakage of melanin into the epidermis induces surrounding cell death as a secondary phenomenon. Melanosome destruction is pulse-width dependent. On the basis of the theory

Curr Probl Dermatol, July/August 1998

TABLE 3. Lasers and light sources for pigmented lesions Laser/light source Wavelength (nm) Q-switched ruby Q-switched Nd:YAG

694 532, 1064

System name

Short pulsed dye Intense pulsed light source

755 755 752 755 510 515-1200

YAG LAZR (Candela) VersaPulse (VPC) (Coherent) ALEX LAZR (Candela) PhotoGenica-T (Cynosure) TATULAZR/Pigmented Lesion Laser (Candela) Pigmented Lesion Laser/TATULAZR (Candela) PhotoDerm PL (ESC)

of selective photothermolysis, pulse durations on the order of 1 microsecond or shorter can selectively damage melanosomes of the order of 1 micrometer in diameter, s1'82 The impact of a short pulsed (<1 gsec) laser on a pigmented lesion produces immediate and temporary whitening that lasts 5 to 20 minutes. An eschar forms and lasts for several days. Histologically, immediate whitening correlates with "ring cell" formation, characterized by the dispersion of pigment in pigmented keratinocytes, melanocytes, and nevus cells to the periphery of the cell. Subsequent sloughing represents epidermal death caused by release of melanin from melanosomes. In the ideal clinical situation only the unwanted pigment is eliminated, whereas the surrounding skin maintains its constitutive pigment. The approach to the treatment of cutaneous pigment depends on the location of the pigment (epidermal, dermal, or mixed), how it is packaged (intracellular or extracellular), and the nature of the pigment. 79 A variety of lasers are used to target melanin in the skin (Table 3). These can be grouped into those that are nonselective, those that are somewhat selective, and those that are highly selective for pigment removal. Epidermal pigmented lesions can be nonselectively removed by using lasers such as the carbon dioxide and continuous visible light lasers that target the epidermis, with a potential risk for dermal damage. To date, only pulsed lasers have been shown to effectively treat both epidermal and dermal pigmented lesions in a safe, reproducible fashion.

Curr Probl Dermatol, July/August 1998

Spot size

28 nsec

5.0 and 6.5 mm

5-7 nsec

532 nm: 2, 3, 4, 6 mm; 1064 nm: 3, 4, 6, 8 mm 2-10 mm

Spectrum RD (Spectrum Medical Technologies-Palomar) Medlite IV (Continuum Biomedical) VersaPulse (VPC) (Coherent)

Q-switched alexandrite

Pulse duration

532 rim: 5 nsec; 1064 nm: 6 nsec 10 nsec 60 nsec 50 nsec 100 nsec 100 nsec 400 nsec 0.5-20 msec

2, 3, 4, mm 2-10 mm 3 mm; 2, 4 mm optional 2, 5 mm 3 mm 3, 5 mm 8 x 35 mm; 8 x 15 mm

Types of Lasers Carbon Dioxide Laser. The carbon dioxide laser emits at 10,600 nm and is well absorbed by tissue water. Resultant superficial absorption allows for nonspecific damage to pigmented epidermal cutaneous structures such as lentigines. Dover et a183 first demonstrated the concept of carbon dioxide vaporization of epidermal pigmented lesions. Ideal treatment parameters use a pulsed laser at low fiuences (<5 J/cm2 at exposure times of 0.1 msec) in a defocused mode with a spot size of 2 to 5 mm. Thermal damage occurs at the basal cell layer, followed by epidermal necrosis and dermal-epidermal separation 24 hours later. 84 Dermal damage can be reduced by use of short exposure times. Although early studies with a low-fluence carbon dioxide laser demonstrated that lentigines could be removed effectively, a controlled comparative study of the carbon dioxide laser, a scanned argon laser, and liquid nitrogen cryotherapy in the treatment of lentigines demonstrated that cryosurgery was approximately 50% better than either of the two laser treatment modalities, with a lower risk benefit ratio. 85 Continuous-Wave Visible Light Lasers. The argon laser emits blue-green visible light at six different wavelengths, with predominant wavelengths at 488 and 514 nm. The beam is continuous, although it can be shuttered. The green blue light is well absorbed by both melanin and oxyhemoglobin, thereby leading to undesired vascular injury. The argon laser can be used to treat epidermal pigmented lesions; however, the resultant nonselective thermal damage makes it less desirable for the treatment of dermal pigmented lesions. 86

149

FIG. 12. Facial [entigines treated with Q-switched ruby laser. A, Before treatment. B, Three months after single laser treatment.

Other continuous-wave and quasicontinuous-wave visible light lasers, such as the argon-pumped tunable dye laser, the krypton laser, and the copper vapor laser, are similar to the argon laser in its effectiveness, side effects, and subsequent limitations. Short Pulsed Lasers. Four different short pulsed lasers have been developed on the basis of the theory of selective photothermolysis to selectively target pigment in the skin. These include three Q-switched lasers (the ruby, neodymium:YAG, and alexandrite lasers) and the short pulsed dye laser at 510 nm. The Q-switched ruby laser uses a ruby (aluminum oxide) crystal to emit light at 694 nm. The Q switching produces pulse durations of 20 to 40 nanoseconds with fluences as high as 10 J/cmZ.87 Light emitted at 694 nm penetrates 1 to 2 mm into the dermis, allowing for treatment of both epidermal and dermal pigmented lesions as well as pigment within hair follicle. Furthermore, 694 nm is considered a therapeutic window for pigment because there is very tittle hemoglobin absorption at this wavelength.

150

The Q-switched Nd:YAG laser emits at 1064 nm, but the frequency can be doubled with a potassium titanyl phosphate crystal, to 532 nm. The 1064 nm wavelength demonstrates poor epidermal absorption; however, limited absorption by deep dermal pigmented entities, such as nevus of Ota, allows for selective disruption of these lesions. 88 Light at 532 nm penetrates only into the upper dermis but is very well absorbed by melanin and hemoglobin. It is therefore effective in treating epidermal and superficial dermal pigmented structures; however, vascular injury is common when this wavelength is used to treat pigmented lesions. The 510 nm pulsed dye laser was developed on the basis of the observation that the most specific epidermal pigment damage occurs at 504 nm. 89 The short pulse duration and subsequent limited thermal damage makes this laser optimally suited for the treatment of epidermal and superficial dermal lesions.

Curr Probl Dermatol, July/August 1998

The Q-switched alexandrite laser is a solid state laser emitting at 755 nm at pulse durations of 50 and 100 nanoseconds. The similarity of this device to the Q-switched ruby laser results in similar clinical results in the treatment of pigmented lesions.

Clinical Applications Treatment of Epidermal Pigmented Lesions With Short Pulsed Lasers. Lentigines are uniformally responsive to all four pulsed lasers (Figure 12). Occasionally, a second or third treatment is necessary for large and resistant lentigines. The efficacy of treatment is inversely proportional to the distance of the lesion from the face. Ephelides (freckles) and lentigines of Peutz-Jeugher's syndrome are also responsive.90-92 Cafe-au-lait macules respond variably (Figure 13). There is one report of complete lightening of all cafeau-lait macules treated with a 510 nm pulsed dye laser with no evidence of recurrence 1 year later. 93 Most studies, however, have demonstrated approximately 50% lightening of cafe-au-lait macules, and in those that have responded 50% show signs of recurrence with any of the short pulsed lasers. 94,95 In general, cafe-au-lait macules require repeated treatments over a period of months or even years to achieve maximal lightening. As treatment progresses, uniform cafe-aulait macules break up into a speckled pattern that eventually clears. Postinflammatory hyperpigmentation is common during the treatment but eventually fades. Although comparative studies are not available, the general clinical impression is that the ruby laser and 510 nm pulsed dye lasers are more effective than the alexandrite laser and the Q-switched Nd:YAG laser at either 532 or 1064 nm. Nevus spilus and Becker's nevi are even more difficult to treat than cafe-an-lait macules are. Total clearing is uncommon, although hyperpigmentation, especially at the edges of the lesions, is relatively common. Another observation is the high rates of recurrence after treatment. %,97 Results of treatment of melasma and postinflammatory hyperpigmentation have generally been disappointing. Although epidermal melasma is responsive to all the short pulsed lasers, it is also effectively treated with topical bleaching agents, limiting the need for laser therapy. Dermal melasma or mixed epidermal and dermal melasma may lighten with treatment with pulsed lasers, but invariably pigmentation recurs with

Curr Probl Dermatol, July/August 1998

Fill. 13, Cafe-au-lait macule treated with Q-switched ruby laser. Before (A) and after (B) laser treatment. (Courtesy of Karen Wiss, MD) There was no recurrence of lesion 3 years after completion of treatment.

sun exposure. Postinflammatory hyperpigmentation has shown temporary improvement and, in the occasional case, total lightening is observed. However, in many cases, hyperpigmentation is actually worsened by treatment. 35,98-I°2 Dermal Pigmented Lesions. Nevus of Ota represents a dermal melanocytosis with increased melanocytes in the reticular dermis and a slight increase in epidermal melanocytes. Until the development of short pulsed lasers there was no effective treatment for nevus of Ota that did not replace the pigmented lesion with scarring. Meticulous studies have demonstrated that all three long-wavelength short pulsed lasers, the Qswitched ruby, the Nd:YAG, and the alexandrite lasers, are effective at treating nevus of Ota with complete or almost complete clearing after several treatments. Although postinflammatory hyperpigmentation is not uncommon during the treatment, once the nevus of Ota has fully cleared the results are usually permanent. 1°3-1°6

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Tattoos. Tattoos can be placed for cosmetic reasons or medical reasons or may result from the accidental penetration of the skin by foreign pigmented material (traumatic tattoo). A number of different modalities have been used for the removal of tattoos, such as surgical excision, dermabrasion, cryosurgery, or destruction with caustic chemicals, yielding variable responses and frequently causing significant scarring. The use of lasers in tattoo removal was first reported by Goldman et 3_1107 in 1967, with use of a non-Q-switched ruby laser, and was refined by Reid et al 1°8 in the 1980s and Taylor et a1119 in 1990. Currently there are several pulsed lasers that can effectively treat tattoos with little scarfing, such as the Q-switched ruby laser (694 nm), the Q-switched alexandrite laser (755 nm), the Q-switched Nd:YAG laser (1064 nm and 532 nm), and the short pulsed dye laser (510 nm). For a laser to be effective in tattoo removal, the light must be absorbed by the tattoo pigment and the pulse duration must be shorter than the thermal relaxation time of the particles. Black tattoo pigment absorbs all laser wavelengths, making it the most susceptible to treatment, whereas colored tattoos selectively absorb laser light and can thus be effectively treated by only some lasers. For example, green tattoo pigment does not absorb green light (532 nm) and has limited absorption at 1064 nm, limiting the use of Nd:YAG lasers. Red pigment tattoos do not absorb 694 or 755 nm light, making the ruby and alexandrite lasers ineffective for treating red tattoos. The mechanism by which the Q-switched lasers remove tattoo pigment is not fully understood. Although some of the tattoo pigment is eliminated externally through scale or crust or through rephagocytosis, histologic studies have shown the presence of a considerable amount of residual tattoo pigment in the treated areas. 11° It is thought that the absorption of laser energy by the pigment particles causes fragmentation of these particles, allowing for their systemic elimination, while leaving behind lamellated pigment material that is less visibly apparent. A pyrolytic chemical reaction induced by the short pulsed light may also play a role in alteration of the particles. Treatment of tattoos with lasers depends on the type of tattoo and its pigment content. Each tattoo may consist of more than one color, and, because there is no single laser that can treat all colors, multicolored tat-

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toos usually require the use of more than one laser for complete removal. Amateur tattoos require fewer laser treatments because they usually consist of a single pigment, which is more easily disrupted by pulses of laser light. Professional tattoos may contain multiple pigments, which are less easily disrupted, requiring more treatments to clear. Blue-black tattoos respond to treatment with the Qswitched ruby laser (694 nm) with amateur tattoos responding more favorably (85% completely removed in an average of three treatments) than professional tattoos (10% completely resolved and 70% partially resolved after an average of six treatments) (Figure 14). 109'111 Green tattoos are less responsive to ruby laser, with 65% of them clearing after six to eight treatments (Table 4). Yellow and red tattoos do not respond to Q-switched ruby laser treatment because the red light is not well absorbed by the pigment particles. The Q-switched alexandrite (755 nm) produces results comparable to those of the Q-switched ruby laser in tattoo removal because of its similar wavelength and pulse duration, m It is best at removing green tattoos. Because of concomitant absorption of melanin by the ruby or alexandrite light, laser treatment can result in hypopigmentation, which is usually transient. The Q-witched Nd:YAG (1064 nm) is also effective for the removal of black tattoos, and it may be more effective in treating deeper tattoos than the ruby because of its deeper penetration into skirl. 113 Despite the decreased skin penetration and the higher absorption by epidermal melanin, the frequency-doubled Q-switched Nd:YAG (532 nm) and flashlamppumped short pulsed dye laser (510 nm) are most effective in the treatment of brighter tattoos colored red, yellow, orange, blue, or violet. 114 Current research efforts are focusing on the use of lasers with shorter pulse durations (picoseconds) for more effective treatment of tattoos. Complications seen with the use of Q-switched lasers in tattoo removal include hypopigmentation, transient hyperpigmentation (about 6%), and, less frequently, scarfing (<5%). The risk of hypopigmentation, which may be permanent, is caused by the absorption and damage to the melanin overlying the tattoo and is highest with the ruby and alexandrite lasers (in approximately 40% to 50% of patients), n5 Hyperpigmentation is usually transient. The risk of scarring appears to be more common in certain anatomic areas (shoulders, chest, ankles) and propor-

Curr Probl Dermatol, July/August 1998

FIG. 14. Amateur tattoo treated with Q-switched Nd:YAG (1064 nm) laser. A, Before treatment. B, After four laser treatments. (Reproduced with permission from Arndt KA, Dover JS, Olbricht SM. Lasers in cutaneous and aesthetic surgery. Lippincott-Raven; 1997.)

tional to the number of treatments delivered. An important adverse effect of Q-switched and pulsed lasers has been noted in the treatment of flesh-colored or pink-red cosmetic tattoos that have iron- or titanium oxide-containing pigments. 116 All lasers with pulse durations less than 1 gsec can cause an immediate posttreatment darkening or blackening of the tattoo pigment, which is believed to result from the reduction of ferric oxide (rust color) to ferrous oxide (black color). This effect does not clear spontaneously and requires either repeated laser treatments or excision of the lesion. It may occur in any tattoo with flesh-colored tones, including tattoos that are a mixture of a fleshtone pigment with a dark pigment (eg, brown tattoo consisting of flesh-tone and black pigments). Local allergic or granulomatous reactions may occur in patients with multicolored tattoos and are usually the result of yellow (cadmium), red (mercury), and blue (cobalt) inks. Systemic allergic reactions may also occur. Patients with a localized granulomatous tattoo are at a high risk for a local or systemic reaction

Curr Probl Dermatol, July/August 1998

from laser-induced release of tattoo antigens. Appropriate anaphylactic measures and premedication with antihistal~fines or systemic corticosteroids should be considered in these cases. Lentige Maligna. Lentigo maligna, the in situ precursor to lentigo maligna melanoma, 117 has been treated with both continuous-wave and pulsed visible light lasers. Current][y there is no consistent role for the use of short pulsed lasers in the treatment of these lesions. Early studies with the argon laser were encouraging, 118 but long-term follow-up reveals that the recurrence rate is at least 50%. 119 A recent study evaluated the use of the Q-switched ruby laser in the treatment of lentigo maligna. Elderly patients with unresectable lentigo maligna were treated with the Q-switched ruby taser with a 5 mm spot, 10 J/cm 2 with three to five overlapping pulses and a centimeter rim of normal-appearing tissue. Although three patients cleared for a total of 9 months to 2 years, one patient's lesion recurred as a melanotic nodule within the lentigo maligna.12o Two further patients treated in

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TABLE 4. Response of tattoos to different types of lasers Type of laser

(wavelength, pulse duration)

Black/blue ink tattoos

Green ink tattoos

Red ink tattoos

Excellent Excellent Excellent Poor Poor

Fair Good Good Poor Poor

Poor Poor Poor Excellent Excellent

Q-switched Nd:YAG (1064 nm, 5 nsec) Q-switched alexandrite (755 nm, 50 or 100 nsec) Q-switched ruby (694 nm, 25 nsec) Frequency-doubled Q-switched Nd:YAG (532 nm, 5 nsec) Short pulsed dye (510 nm, 500 nsec)

a similar fashion have also had recurrences (Dover, unreported observation). On the basis of the results of these preliminary studies, further investigation will be required before laser treatment can be considered helpful for treatment of lentigo maligna. Nevoeellular Nevi. Congenital nevomelanocytic nevi are present at birth and vary in size from small (<1.5 cm) to medium (1.5 to 19.9 cm) to giant (>20 cm). The potential for melanoma development in congenital nevi increases as the size of the nevus increases. 121 The treatment of choice for removal of congenital nevi is surgical excision. Although this is effective in most instances, congenital nevi in cosmetically sensitive areas, such as on the face or in the genital area, are difficult to treat surgically and for that reason laser treatment has been evaluated. Clinical lightening has been observed with the Q-switched ruby and Qswitched Nd:YAG laser (1064 nm), 122,123 but repigmentation has been frequent (Dover, unreported observation). More recently, longer pulsed ruby and alexandrite lasers have been developed for laser hair removal. Studies on laser tissue interactions and experience from Asia suggest that the alexandrite laser may be much more effective than Q-switched sources in the treatment of deep pigmented structures such as congenital and acquired nevi. 124,125

Lasers for Skin Resurfacing Carbon Dioxide Laser The carbon dioxide laser, which was first developed in 1964, is one of the most widely used lasers in dermatologic surgery. It emits infrared light at a wavelength of 10,600 nm, which is primarily absorbed by water. Because infrared radiation is invisible, a red (633 nm) helium neon beam or a red diode laser serves as its aiming beam. Carbon dioxide lasers rapidly heat and vaporize intracellular water, resulting in tissue destruction. The

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Bright-colored tattoos (purple, blue, yellow) Fair Fair Fair Good Good

water content of the target tissue determines the depth of penetration of this wavelength. Ninety percent of all the energy is deposited in the first 0.1 mm of skin, using a 0.2-second exposure time and a 1 mm spot size. 126 However, because of heat diffusion, thermal coagulation occurs up to a depth of 1 mm. The first carbon dioxide lasers developed emitted a continuous-wave beam. They had the ability to cut or vaporize tissue. At the focal point they generate high fluences that cut through skin. When the handpiece is pulled away from the skin, thus defocusing the beam, the spot size increases, the fluence decreases, and tissue is vaporized. The greatest advantage of this laser in incisional surgery is the improved hemostasis it affords. The carbon dioxide laser coagulates and seals blood vessels 0.5 mm in diameter or less. 127With better hemostasis, visibility is improved and operative time is shortened considerably. This is beneficial for anticoagulated patients and is advantageous for the excision of vascular lesions. It has also been found to seal small nerve endings 128 and lymphatics, 129 resulting in less postoperative pain and edema, and subsequently shortened recovery time. An added advantage is its safety in patients with cardiac pacemakers or monitors. A disadvantage of carbon dioxide laser incisions is delayed wound healing and a higher rate of wound dehiscence because of residual thermal damage. Tensile strength of wounds during the first 3 weeks after carbon dioxide incisional surgery is reduced compared with cold steel incisions. 13° The continuouswave carbon dioxide laser has also been used as a vaporizing tool for the treatment of epidermal and even superficial dermal lesions. Although results in expert hands are impressive, the potential for extensive thermal coagulation leading to unacceptable rates of scarfing has limited its use. Laser Resurfaeing. Recently there has been a surge of public interest in skin rejuvenation. Conventional methods used for treating photodamaged skin include chemical peels, dermabrasion, and cosmetic surgery such as face-lifts. In the 1980s and early 1990s contin-

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TABLE 5, Features of carbon dioxide and erbium:YAG lasers Carbon dioxide laser

Wavelength Depth of penetration Ablation threshold Advantages

Disadvantages

Indications

Erbium:YAG laser

10,600 nm 20 gm 5 J/cm 2 More dramatic results Skin tightening Hemostasis More clinical experience More recovery time Anesthesia required Photoaging (mild to severe) Acne scarring Actinic chelitis Epidermal lesions (eg, appendageal tumors) Incisional surgery--blepharoplasty, hair transplants, endoscopic rhytidectomy

uous-wave carbon dioxide lasers were used to resurface photodamaged skin in a procedure called thermabrasion. However, this procedure was associated with an unacceptably high risk/benefit ratio. Dwelling too long on a specific area results in significant thermal diffusion, excessive thermal damage, and resultant scarring. For laser resurfacing to be effective, selective thermal destruction based on the principles of selective photothermolysis 1° is required. To control the depth of thermal damage that occurs in tissue, the appropriate pulse duration should be less than 1 millisecond and to achieve tissue vaporization sufficient energy must be delivered within this time. With a pulse duration of less than 1 millisecond, carbon dioxide laser light penetrates only 20 gm into tissue, and thermal damage can be confined to less than 100 gm of tissue. TM The estimated ablation threshold is 5 J/cm 2 132. Less energy will produce diffuse tissue heating without vaporization. The development of newer pulsed and scanned carbon dioxide lasers that allow precise removal of layers of skin with limited thermal conduction to surrounding tissues has resulted in efficient tissue vaporization with greater control of depth of thermal damage (Table 5). This has generated a significant increase in interest in laser resurfacing from physicians belonging to a wide range of specialties. Laser Technology. Several carbon dioxide lasers are currently available that achieve well-controlled tissue ablation for resurfacing. One group is made up of the pulsed carbon dioxide lasers, which deliver energy in individual pulses about 1 millisecond or

Curr Probl Dermatol, July/August 1998

2940 nm 3 gm 1.5 J cm 2 More efficient ablation Wiping between passes unnecessary Less recovery time Less painful, lower anesthesia requirements No evidence of collagen shrinkage or skin tightening More passes may be necessary Minimal hemostasis Mild photoaging Mild acne scarring Actinic cheilitis Epidermal lesions Dermal lesions (eg, appendageal tumors) Potentially useful for neck, chest, hands

less. The Coherent Ultrapulse (Coherent Medical, Pale Alto, Calif.), which was the first developed and most extensively studied, produces up to 500 mJ of energy in each 600 microsecond to 1 millisecond pulse. Vaporization can be performed either with a 3 mm spot size or by computer pattern generator, which can deliver various patterns of up to 80 pulses, each pulse measuring 2.25 mm in diameter. The Tru-Pulse carbon dioxide laser (Palomar Medical Technologies, Beverly, Mass.) delivers 500 mJ of energy at a 3 m m square spot size with a much shorter pulse duration of 60 microseconds. Less tissue is ablated per pass, and to produce improvement equivalent to that of the Ultrapulse more passes are required; the resultant wound and time to healing are similar. Superpulsed carbon dioxide lasers that are marketed for resurfacing include the NovaPutse (Luxar Corporation, Bothell, Wash.) and the Paragon ClearPulse (Laserscope, San Jose, Calif.). Both of these laser systems cleanly vaporize tissue but only with spot sizes on the order of 1 mm, thus limiting the speed of resurfacing. Scanning devices have been developed to improve their speed and reproducibility. Another way to achieve well-controlled tissue ablation is to rapidly scan the focal spot of a focused continuous-wave carbon dioxide laser over the skin. The Sharplan Silktouch and Feathertouch flashscanners (Sharplan Lasers, Allendale, N.J.) have computer-driven mechanical devices that scan a 0.2 mm spot in a spiral manner ranging in diameter from 8 to

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16 m m in several shapes at a constant velocity so that no individual spot is irradiated more than once and the dwell time on any individual spot is less than 1 millisecond while achieving fluences above the ablation threshold. The Silktouch flashscanner scans the shape twice with a tissue dwell time of less than 1 millisecond, whereas the Feathertouch flashscanner scans the pattern just once at more than twice the speed, resulting in a tissue dwell time in the range of 0.3 milliseconds. In the Feathertouch mode the wattage used is doubled to keep the energy fluence delivered to the tissue above the 5 J/cm 2 vaporization threshold. The amount of tissue vaporized per pass and the zone of thermal damage are both greater with the Silktouch flashscanner. Indications. The two most common indications for laser resurfacing are photoaging and scarring. Rhytides can be classified into two: nonmuscular (static) or dynamic. Nonmuscular rhytides result from excessive sun exposure and are most prominent in the periorbital and perioral areas. These appear as fine wrinkling and respond very favorably to resurfacing. Dynamic creases, which are seen in the forehead, glabella, and nasolabial folds tend to be more resistant and recur frequently because Of the unavoidable effects of muscle contraction. These movement associated wrinkles respond best to botulinum exotoxin A (Botox) injections. Dyspigmentation of photodamage also improves with resurfacing. Laser resurfacing is effective for both acne scars and hypertrophic traumatic and surgical scars. Ideal ache scars are distensible scars that are either modestly deep or slightly elevated. Excision of deep-pitted and bound-down scars is required for resurfacing to achieve more optimal results. Because laser resurfacing is relatively bloodless and allows controlled tissue removal resulting in a shortened healing time and lower risk of scarring, it is also used to treat rhinophyma, diffuse actinic cheilitis, actinic keratoses, and epidermal lesions such as epidermal nevi, syringomas, xanthelasma (Figure 15), sebaceous hyperplasia, and benign compound nevi. Scars resulting from varicella, trauma, and surgery also improve significantly. Potential Contraindications. The ideal laser resurfacing candidate is a healthy, fair-skinned patient with realistic expectations. Patients who are keloid formers are not routinely treated. Treatment of patients who

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have taken oral retinoids (Accutane) within the past 2 years is postponed because this has been associated with atypical scarring. 133 Patients who have received previous radiation therapy, deep chemical peels, and dermabrasion are treated more cautiously because the absence of appendageal structures may preclude rapid or complete healing. Skin that has been recently undermined, as in face-lift or blepharoplasty, has an altered blood circulation for several months. Resurfacing procedures performed at the same time or soon after undermining increase the risk of skin necrosis with associated scarring; thus we recommend that laser resurfacing of undermined skin be deferred for 6 months after the original surgical procedure. Hands, necks, and chests are not resurfaced with the carbon dioxide laser because of the unacceptably high risk of scarfing. Preoperative Course. Patients are advised to use tretinoin for at least 4 to 6 weeks before resurfacing. Although this has been shown to speed reepithelializadon after dermabrasion TM and chemical peels, controlled studies have not yet been performed in resurfacing. Patients with Fitzpatrick skin type III or darker are also started on hydroquinone cream several weeks before resurfacing to minimize postinflammatory hyperpigmentation. All patients are started on prophylactic oral antivirals such as acyclovir, famciclovir, or valaciclovir 1 day before resurfacing. Oral antibiotics such as dMoxacillin or azithromycin are also routinely prescribed to reduce the chance of secondary bacterial infection. Anesthesia. For patients who undergo treatment of limited areas, such as the eyes or mouth, local anesthesia is sufficient. Those who undergo full-face carbon dioxide laser resurfacing require either intravenous sedation with or without added regional and local anesthesia or general anesthesia. Technique. In carbon dioxide laser resurfacing, single vaporizing laser pulses with minimal overlap is performed followed by wiping of the desiccated proteinaceous debris with saline solution-soaked sponges. Once this debris has been wiped away, a dry gauze is used to remove any water remaining on the skin surface because this will absorb the laser energy and block its reaction with dermal tissue. A second laser pass is then performed over the entire area of photodamaged epidermis. If necessary, additional laser passes are performed over the entire area. With each additional pass, there is further wrinkle smoothing and increased risk of complications

Curr Probl Dermatol, July/August 1998

because of the greater depth of tissue injury. Subsequent passes are concentrated on high points of scars or shoulders of rhytides. One of the end points of treatment is smoothing away tissue irregularities and visible wrinkle lines so that a smooth and even surface results. Finally, to blend or soften lines of demarcation, feathering of borders is performed by decreasing the pulse energy and density of puls, es.

Postoperative Course. Swelling, oozing, and crusting are expected during the first 1 to 3 days. Swelling is often most severe on the second and third postoperative days and can be controlled with ice packs, head elevation at night, and oral corticosteroids. Patients are advised to apply cool compresses to the treated areas frequently for the first week to remove the serous exudate and any residual necrotic debris. Between soaks, the area is kept moist with petroleum jelly (Vaseline) or Aquaphor healing ointment (Beiersdorf-Jobst, Norwalk, Conn.) or with a bioocclusive dressing such as Second Skin (Spenco Medical, Waco, Tex.), Vigilon (Bard Patient Care, Murray Hill, N.J.) or Flexzan (Polymedica Industries, SugarLand, Tex.). Topical antibiotics such as Polysporin are not routinely prescribed because of the high incidence of allergic contact dermatitis associated with their use. Ninety percent of patients have little discomfort. The others require narcotic analgesics. After resurfacing, there is a variable period of erythema ranging from 6 to 12 weeks, which is easily camouflaged with a green-based make-up. Response Rates. Results from use of all the described carbon dioxide laser systems are comparable in expert hands, whereas techniques with each vary greatly. Early results of laser resurfacing have been very impressive. Although assessments have not been uniform, all reports have shown significant improvement of photoaged skin (Figs. 16 to 18). 135137 Most patients with wrinkles attain a 50% to 90% improvement. Laser resurfacing is, however, a relatively new technique started about 5 years ago and no one can say exactly how long the effects will last. Although the earliest patients treated have maintained significant improvement 5 years later, long-term studies have not been completed. The improvement is usually so dramatic that, although wrinkling redevelops, it probably never reaches the degree that it was before laser resurfacing.

Curr Probl Dermatol, July/August 1998

FIG. 15. Xanthelasmas and dark infraorbital circles and wrinkles treated with UltraPulse carbon dioxide laser. A, Before treatment. B, One week after laser resurfacing. C, Three months postoperatively.

Laser treatment of acne scars has not been as successful (Figure 19). Severe acne scars do not respond as favorably as mild to moderate acne scars. Alster and West138 reported 81.4% improvement in clinical and textural appearance of moderate atrophic scars, whereas Apfelberg 139reported that only 2 of 4 patients with severe

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C FIG. 16. Full-face resurfacing of severely photodamaged skin with Coherent UltraPulse carbon dioxide laser. A, Before treatment. B, Three days after procedure. C, One week postoperatively. D, Eight weeks postoperatively, showing significant effacement of rhytides without any pigment or textural changes.

158

Curr Probl Dermatol, July/August 1998

FIG. 17, Full-face resurfacing of severely photodamaged skin with UltraPulse carbon dioxide laser. A, Before treatment. B, Eight weeks after procedure.

acne scarring showed a good result. Skin with supple easily distended scars respond best to resurfacing. Adverse Effects. Side effects after carbon dioxide laser resurfacing are frequent and predictable. Similar to those after chemical peels and dermabrasion, complications are less common and care preventable if excellent technique is followed and postoperative management is fastidious. Adverse effects can be divided into five categories: immediate, predictable effects; infectious effects; eczematous effects; follicular effects; and scarring and pigmentary changes (Table 5). Erythema lasting, on average, 6 to 12 weeks is universal and is considered part of the normal healing process. Erythema and flushing, which develop in the treated site with exertion or emotional upset, are frequent for a year after resurfacing. Some individuals have persistent continual erythema lasting up to 12 months. This may be related to the depth of ablation. The most common adverse effect of laser resurfacing is postinflammatory hyperpigmentation. Transient hyperpigmentation has been reported in up to 36%

Curr Probl Dermatol, July/August 1998

patients. It is most often seen in patients with Fitzpatrick's skin type HI to VI. 140 The hyperpigmentation is more frequent and severe during the summer months and year round in sunny areas. More recent studies demonstrate rates of hyperpigmentation as low as 2.8% in patients pretreated with bleaching creams and retinoic acid. At the first sign of hyperpigmentation, bleaching creams and Retin-A are restarted and sun exposure is avoided. If treatment is started early enough, the hyperpigmentation usually resolves within a few months. Permanent hypopigmentation developing up to 12 months after resurfacing has been reported in 16% of patients and appears to be less frequent than after dermabrasion or deep chemical peels. This hypopigmentation ranges from pale new "sun-protected" skin to white, depigmented skin. Patients with actinic damage may develop a color mismatch between the pale new skin of the resurfaced area and the surrounding sundamaged areas that may include ephelides and lentigines. This mismatch is minimized by resurfacing the entire face, or at least entire cosmetic units, and feath-

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FIG. 18. Perioral rhytides and photodamage treated with the UltraPulse carbon dioxide taserl A, Before treatment. B, Three months postoperatively.

ering the treatment into the surrounding areas. Future sun exposure will also help to blend the resurfaced skin by developing new lentigines and ephelides. Mifia are a result of follicular reepithelialization compounded by the use of occlusive moisturizers. Acne is a frequent postoperative event, especially in patients with a history of acne. It usually develops in the first few weeks after resurfacing and responds to standard ache treatment. Contact dermatitis, noted with the use of some topical anesthetic preparations, does not correspond with patch test findings but resolves with appropriate treatment. This occurrence increases the chances of postoperative erythema and hyperpigmentation. Eczematous dermatitis occasionally develops in the first 4 weeks after treatment. It responds rapidly to moisturizers and topical midpotency corticosteroids. Infrequently perioral der-

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matitis develops 1 to 3 months after resurfacing of the perioral region. This is easily controlled with tetracycline and is usually self-limited. In a procedure that removes the epidermis and part of the dermis, infection is a concern. Laser surgeons have learned from experience with dermabrasion and have avoided bacterial infection through the judicious use of antibacterials. Antiviral chemoprophylaxis was originally confined to those with a history of herpes simplex infection, but results suggest that subjects with no history of infection frequently have herpes simplex activation in treated areas. 141 It is now standard practice to use antiviral prophylaxis in all laser resurfacing patients. Yeast infections have occurred but respond well to treatment. Hypertrophic scarring is seldom seen after laser resurfacing. Scarring from laser resurfacing appears to be rare and, with proper patient selection, being conservative with the number of laser passes, and good postlaser wound care, should further reduce the risk. It results from a large number of passes or use of excessive energy and from pulse stacking (overlap of laser irradiated sites, especially after the 1st pass) resulting in excessive thermal damage. It is better to do a touch-up procedure down the road than to go too deeply the first time in an attempt to totally eradicate the offending rhytides. Any areas that may be developing scar tissue should be promptly treated with topical and intralesional corticosteroids, Silastic silicone rubber (Dow Coming, Midland, Mich.) gel sheeting and pulsed dye laser photocoagulation. Although the risk/benefit ratio of carbon dioxide resurfacing appears to be low, it is clear that technique, experience, and postoperative care are essential for a successful outcome. M e c h a n i s m of Action. Several mechanisms are involved in resurfacing. First is ablation of the photodamaged skin. Resurfacing removes the entire epidermis and at least part of the superficial and mid dermis. This is accompanied by significant collagen shrinkage, which occurs when collagen is exposed to temperatures as low as 60 ° C. 142 As much as a two thirds reduction in its original length has been shown to lead to skin tightening. Finally, new collagen formation and alteration of elastin in the dermis occur and is most likely responsible for the continued improvement seen weeks after resurfacing. 143

Erbium:YAG Laser The erbium:YAO laser emits infrared fight at a wavelength of 2940 nm, which is close to the absorption peak of

Curr Probl Dermatol, July/August 1998

FIG. 19. Full-face resurfacing of young patient with acne scarring treated with UltraPulse carbon dioxide. A, Before treatment. B, One year after resurfacing.

water. This results in an absorption coefficient that is 10 times that of the carbon dioxide laser. The erbium laser's depth of penetration is limited to about 3 gm of tissue versus the 20 ~tm penetration depth of the carbon dioxide laser, 144 resulting in more precise ablation of skin with minimal thermal damage to the surrounding tissues. With an energy fluence of 5 J/cm2 the epidermis is vaporized away in four passes. At 8 to 12 J/cm 2 the epidermis is entirely vaporized in two passes. Additional passes are performed until the lesion or rhytid has been effaced, bleeding occurs, or a maximum safe number of laser passes has been completed. Because the procedure is less painful than carbon dioxide laser resurfacing, some patients may tolerate the procedure with oral sedation and a topical anesthetic such as EMLA cream whereas others require local or regional anesthesia with or without oral or intravenous sedation. While erbium laser skin resurfacing appears to be ideal in patients with mild to moderate photoaging (Figure 20), results of erbium laser resurfacing are not as impressive as those with carbon dioxide laser resurfacing in patients with moderate to severe photoaging or

Curr Probl Dermatol, July/August 1998

with moderate acne scarring. To attain results comparable to those of the carbon dioxide laser, an increased number of passes are required, leading to similar healing times. The absence of thermal injury with the erbium laser accounts for the absence of tissue shrinkage at the time of surgery. Whether shrinkage occurs with wound healing after erbium laser resurfacing, yielding skin tightening, remains unknown. Because recovery time is considerably reduced, it is also indicated for patients who need to return to work after 1 week. The erbium laser appears to be useful for resurfacing of nonfacial photodamaged areas, including the necks, hands, and chest. Improvement in these areas after gentle treatment is in dyspigmentation and epidermal texture but wrinkling and creases are not improved. Aggressive treatment in these areas will yield scarring not dissimilar to the results of carbon dioxide laser resurfacing in these areas. This laser may potentially debulk and flatten scars with a minimal risk of scarring. Fifty percent to 95% clearing of hypertrophic scars after three to four treatments has been reported in a small cohort of patients. 145

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FIG. 20. Erbium:YAG laser resurfacing. A, Before treatment. B, After treatment. (Courtesy of Khalil Khatria, MD.)

Further studies to determine the effectiveness of this laser are underway. The main advantage of the erbium:YAG laser is thought to be the potential for an improved side effect profile. The procedure is less painful and may be completed under topical anesthesia. There is less oozing and crusting and the subsequent erythema, although dependent on the number of passes, is shorter lasting than that after carbon dioxide laser treatment. It is unclear whether, depth for depth, the duration of healing and erythema are any shorter. It is too early to tell whether the rate of permanent hypopigmentation and scarring will be any less after erbium:YAG laser resurfacing. When superficial lesions are treated, scarring and hypopigmentation would be unlikely to develop because there is very little thermal damage left behind. However, the end point of treatment is often not clear-cut and the erbium:YAG laser, unlike the carbon dioxide lasers, ablates additional tissue with each laser pass, making it possible to ablate all the way into the fat with resulting scarring. Therefore the number of passes and energy fluence have to be carefully kept track of when the erbium:YAG laser is used. Laser-Assisted Hair Transplantation. Carbon dioxide and erbium:YAG lasers can be used to create recipient sites for hair transplantation. The main advantage of using the carbon dioxide laser is that vessels less that 0.5 mm in diameter are sealed. Thus

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bloodless recipient sites can be created, leading to a significantly shortened operative time, less hair compression, and less handling of grafts during insertion, which theoretically should result in increased hair growth. A potential drawback of carbon dioxide laser-assisted hair transplantation is the adjacent zone of thermal injury created in the recipient site. If this zone of thermal damage is too wide, impairment of revascularization of grafts may occur, compromising graft survival. Studies comparing conventional micrografting and minigrafting versus carbon dioxide laser vaporization have shown conflicting results in terms of hair regrowth. A prolonged healing time has also been observed in laser vaporization sites. Although the erbium:YAG laser has the advantage of leaving a very small zone of thermal damage, resultant hemorrhage interferes with the grafting.

Other Cutaneous Conditions for Which Lasers Are Useful Clinical applications of the different lasers have expanded greatly. Lasers have been used successfully as treatment for conditions that were unresponsive to conventional therapies and as adjuncts to surgical procedures. Such indications include hypertrophic scars and keloids, striae, warts, hair removal and transplantation, and incisional surgery.

Curr Probl Dermatol, July/August 1998

FIG. 21. Extensive plantar warts of sole of foot treated with PDL. A, Before treatment. 13, After laser treatment. (Courtesy of Dr. lan Webster.)

Hypertrophic Scarsand Keloids Despite recent advances on the mechanisms of wound healing, treatment of hypertrophic scars and keloids remains difficult. Various treatments such as intralesional corticosteroids with and without 5-fluorouracil, cryotherapy, radiotherapy, dermabrasion, pressure dressings, silicone gel sheeting, and surgical excision have been tried; however, results have not been very encouraging. Aside from not being very effective, many scars have been worsened by some of these modalities. Ablative Lasers. Continuous-wave lasers, such as the carbon dioxide, argon, 146-148 and Nd:YAG laser 149 were the first lasers used for treating scars. However, these lasers cause nonselective tissue ablation and have resulted in recurrences or worsening of the scars within a few years of treatment. Flashlamp-Pumped Pulsed Dye Laser. Successful laser treatment of hypertrophic scars with use of the PDL was first reported by Alster et al. 15° Hypertrophic scars induced by argon laser treatment of port-wine stains

Curr Probl Dermatol, July/August 1998

underwent five treatments with PDL over a 10-month period. Aside from decreasing erythema, normalization of skin surface texture was also observed. Subsequently, there have been more reports of success in treating hypertrophic scars and keloids resulting from sternotomy, 151 surgical excision, trauma, 152 bums, 153 and ache 154 with the P D L Clinical response rates are 57% to 83%. Multiple treatments are usually necessary, especially with thick or keloidal scars. Adjunctive therapies, such as intralesional steroids, may hasten the improvement of these scars. Transient postinflammatory hyperpigmentation has been the most common adverse effect reported. Hypertrophic scars and keloids often manifest a prominent erythematous color. This is the result of angiogenesis associated with wound repair. It is not clear how the PDL works in the treatment of scars. It may, however, be related to selective destruction of vascular structures in the scars. Destruction of this vasculature may lead to tissue ischemia, which results in altered collagen metabolism and release of collagenase. Alternatively, thermal conduction to the surrounding dermis may modify its collagen composition.

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Finally, the increase in the number of mast cells after laser treatment may play an imPortant role. Histologically, aside from disappearance of dilated vascular channels, 15° laser-irradiated scars showed a normal number of dermal fibroblasts within looser, less coarse collagen fibers and an increase in number of mast cells. 151 A recent study performed on hypertrophic scar tissue implanted in athymic mice showed that the extent of inhibition of growth of the scar tissue correlated with the extent of vascular damage which was maximal at the highest fluence used (10 J/cm2). 155 Despite the presence of numerous studies in which the PDL was used in treating scars, several questions remain unanswered. The ideal time to initiate laser treatment and the ideal number and frequency of laser treatments are undefined. Complete remodeling of scars usually takes 12 months to occur; however, in keloid-prone individuals it is possible that early treatment would prevent their formation. Hypertrophic scars predictably do better than keloids.

Striae Although primarily of cosmetic concern, there has been considerable demand for the treatment of striae. Aside from topical tretinoin, which has shown conflicting resultS, no other treatment options are available. Pulsed Dye Laser Treatment. Because striae have been considered as a type of scar and hypertrophic scars and keloids have responded well to PDL treatments, it is assumed that PDL would also improve striae. McDaniel et al51 were the first to report the effectiveness of PDL (450 gsec, 585 nm) treatments in improving striae. They found the 10 mm spot size with use of 3.0 J/cm 2 fluence to be most effective. Improvement was seen clinically and by optical profilometry. Histologically, an increase in elastin content was observed. Further research has shown that smaller striae respond better than large striae, whereas location and age of the striae did not affect the response rate. 156 Increased elastin may be responsible for the improvement, and this may be explained by the fact that visible light lasers, at low fluences, stimulate fibroblast proliferation, which enhances secretion of growth factors, and collagen production. 157,158

Warts Warts are extremely common, affecting approximately 10% of children and young adults. Although more commonly of cosmetic significance, some warts, espe-

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cially periungual and plantar warts, may be associated with pain and interfere with function. Several therapies have been used in the treatment of warts including caustics such as salicylic and lactic acid, liquid nitrogen, electrocautery, and surgical excision. However, all these cause nonspecific tissue destruction and are associated with a risk of bleeding, infection, and scarring. Response rates range from 56% to 67%. 159,16° C a r b o n Dioxide Laser. The carbon dioxide laser has been used for treating various cutaneous disorders for more than two decades. Advantages of this modality include well-controlled tissue destruction and hemostasis. However, reported side effects include significant postoperative pain, infection, delayed bleeding, nail dystrophy, and scarring. The carbon dioxide laser is advantageous in treating periungual and plantar warts and condyloma acuminata. Periungual warts are difficult to treat because they frequently extend between the nail fold and nail plate and into the lateral horn of the nail matrix. The carbon dioxide laser has the advantage of vaporizing these areas without the need for nail avulsion. However, permanent onychodystrophy is frequent. Plantar warts are usually associated with an overlying callus, which when shaved off show multiple small block dots representing thrombosed capillaries. The carbon dioxide laser is able to precisely destroy this tissue in an efficient manner. Care must be taken because the risk of scarring exists. To efficiently remove adequate tissue, the continuous-wave laser mode is usually used. Paring of the overlying hyperkeratotic tissue may be helpful. Successive laser passes are usually necessary with debridement and curettage performed in between to remove any charred debris. Response rates for carbon dioxide laser treatment of warts range from 32% to 81%. 161-163 This moderate response may be related to the presence of wart virus in normal-appearing epidermis, 5 to 10 mm from the clinical lesion. 164 Thus a treatment margin of at least 1 cm of normal skin is essential to achieve cure. Another risk of this procedure is the presence of viable human papillomavirus particles in the laser plume of vaporized warts. 165 Whether this may cause transmission of the disease remains to be seen; however, appropriate precautions should be taken to minimize the risk of contact with these viral particles. Pulsed Dye Laser. The dermis underlying epidermal verrucous changes demonstrate dilated and con-

Curr Probl Dermatol, July/August 1998

TABLE 6. Lasers and light sources used for hair removal

Laser/light source Long-pulse ruby

Long-pulse alexandrite

Q-switched Nd:YAG

Intense pulsed light source

Wavelength (rim)

System name

Pulse duration

Fluence (J/cm 2)

Spot size (ram)

694

Epilaser (Palomar)

3 msec

10-40

7, 10

Epitouch (Sharplan)

1.2 msec

10-40

3-6

Chromos 694 (MEHL Biophile) PhotoGenica LPIR (Cynosure)

850 gsec

5-20

7

5, 10, 20 msec

10 nsec

40 25 30 10-50 10-45 10-50 10-25 2-3

7 10 6 x 10 8, 10 12 5 7 7

2.5-7 msec

30-65

8 x 35 10 x 45

755

1064

590-1200

Gentlelase (Candela)

3 msec

Epitouch ALEX (Sharplan) Softlight (Thermolase)

2 msec

EpiLight (ESC)

gested vasculature in the papillae extending up to the elongated rete ridges. The PDL, which selectively destroys superficial dermal capillaries, may effectively treat warts. Garden et a121 were the first to report success in using this modality for recalcitrant verrucae. Of 39 patients treated with a 5 mm spot size at a fluence of 6.25 to 7.5 J/cm2,166 (72%) were cleared of their warts at an average of 1.68 treatments. Overall response rates ranging from 83% to 99% has also been reported (Figure 21). 167 However, recent reports have been less impressive. 168,169 The exact mechanism of action has not been fully explained. Although 585 nm light is well absorbed in dermal vasculature, repeated pulses of a PDL produces nonspecific thermal damage of the epidermis and dermis. Currently it is believed that the PDL primarily acts by thermal destruction of the wart. Other proposed mechanisms include vascular damage and an immune-mediated mechanism. Optimal treatment parameters are double or triple pulses at 1 Hz with a 5 to 7 mm spot size at fluences of 7 to 9 J/cm 2. Paring the wart before laser treatment enhances laser light penetration, but bleeding should be avoided and controlled with aluminum chloride because surface blood absorbs laser light. Treatment is uncomfortable and may require anesthesia. After treatment lesions appear gray to purpuric, followed by a blackish eschar lasting 1 to 2 weeks. Multiple treat-

Curr Probl Dermatol, July/August 1998

Other features EpiWand (patented cooling contact handpiece) Dual mode; may also be Q switched

Cooling tip available

Dynamic cooling

Carbon suspension applied several minutes before treatment acts as chromophore

ments, performed every 2 to 6 weeks, are often necessary. Risks such as scarring, infection, or bleeding a r e minimal. The cost effectiveness of PDL treatment of warts remains unknown. Further study documenting its effectiveness in the treatment of simple and complicated warts is necessary before its role in our therapeutic armamentarium is known.

Hair Removal Laser hair removal has received immense media attention. Conventional methods such as shaving and epilation are temporary, and although electrolysis is permanent it is tedious, uncomfortable, and only 15% effective. Despite all the media hype, very little published data are currently available. Traditional thinking was that the hair shaft was produced by rapidly dividing matrix stem cells located in the deepest portion of the hair follicle, 2 to 7 m m below the Skin surface. However, recently it has been suggested that follicular stem cells are located near the insertion of the arrector pill muscle, in the area known as the bulge, which is 1 to 1.5 m m deep. 17° Thus for effective hair removal to occur, it may be necessary destroy both the bulge and dermal papilla. Our concept for understanding laser hair removal is based on the principles of selective photothermolysis. In the case of hair removal, the chromophore is

165

FIG. 22. Facial hyperLrichosis treated with normal-mode ruby laser. A, Before treatment. B, Three months after single laser treatment. (Courtesy of Drs. Christine Dierickx and R. Rox Anderson.)

melanin and the pulse duration should be close to the thermal relaxation time of the hair follicle, which ranges from 1 to 10 milliseconds. Q-Switched Lasers. Q-switched Nd:YAG and ruby lasers, which selectively target melanin, are effective for treating various pigmented lesions and tattoos. Although these lasers have been demonstrated to decrease hair regrowth after aggressive treatment, 171,172 their pulse duration is too short to effectively destroy the hair follicle. Normal-Mode Lasers. Longer pulse duration, nonQ-switched lasers make more sense as tools to induce permanent hair loss (Table 6). The ruby laser, which emits at a wavelength of 694 nm, is selectively absorbed by melanin and penetrates deeply into the dermis. In early studies, Grossman et a1173 used a normal-mode ruby laser with a spot size of 6 to 8 mm, pulse duration of 0.3 milliseconds, and fluence of 30 to 60 J/cm 2. Results showed a significant delay in hair growth in all laser-treated sites compared with shaven

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and epilated control sites. Six months after a single treatment only sites that received the highest laser fluence showed significant hair loss. Permanent hair removal was seen in 2 of the 12 subjects treated. Fifty percent to 70% reduction in hair growth 6 months after one to two treatments has also been reported with a 0.3 to 1.0 millisecond normal-mode ruby laser 174. More recent studies of Dierickx 175 have demonstrated that long pulse ruby lasers can induce growth delay and permanent hair removal. The growth delay occurs in all patients, no matter what hair color, at various fluences and lasts for 1 to 3 months depending on the anatomic region treated. Permanent hair removal occurs primarily among dark-haired individuals and requires fluences of 30 J/cm 2 or greater (Figure 22). Hair follicles at the early anagen phase are most sensitive to damage. Hairs that regrow after laser treatment appear lighter in color and finer (vellus hairs). Histologically, clinical alopecia is characterized by either a miniaturized hair follicle or complete destruction of the hair follicle. Long pulse durations close to the thermal relaxation time of the hair follicle (1 to 10 msec) and high fluences are most effective at hair removal. Several currently available lasers approved by the US Food and Drug Administration produce 0.3 to 3 millisecond, high-energy pulses at fluences ranging from 10 to 75 J/cm 2. A normal-mode alexandrite laser that emits at a wavelength of 755 nm at fluences ranging from 10 to 40 J/cm a and pulse durations of 5, 10, or 20 milliseconds also effectively reduces hair growth. Because 694 and 755 nm light targets melanin, which is also present in the epidermis, epidermal damage may occur. To minimize epidermal damage, a contact handpiece that cools the epidermis and maximizes light penetration to the deeper dermis is used in conjunction with some commercially available devices. Other systems deliver pulses through a cooling gel that absorbs epidermal heat. The ideal patient is a fair-skinned individual with darkly pigmented hair. However, for darker-skinned individuals, pretreatment with a bleaching cream, tretinoin, and a sunscreen may make the treatment safer and more effective. Multiple treatments appear to increase treatment efficacy. Possible risks of this procedure include hypopigmentation or hyperpigmentation, which is usually temporary, and scarfing. Because the hair follicle is surrounded by nerve endings, treatments may be painful. Topical or local anesthesia is required in some

Curr Probl Dermatol, July/August 1998

individuals and in sensitive anatomic sites such as the upper lip. Laser-Assisted Hair Removal. For selective photothermolysis to occur, a target chromophore that absorbs the laser light is necessary. Most hair removal laser systems use melanin, which is endogenous. However, the chromophore may also be introduced into the hair follicle. The Softlight system involves topical application of a suspension of carbon particles to wax-epilated skin, which is then wiped off and irradiated with a Q-switched Nd:YAG laser (1064 nm) with a pulse width of 10 nanoseconds at fluences of 2 to 5 J/cm 2. The interaction between the carbon particles and the laser light results in thermal and mechanical damage to the hair follicle. Because the target chromophore is exogenous in origin, this technique should be potentially effective in treating both light and dark skin types and both dark and light hair. Initial reports demonstrate diminution of hair regrowth after several treatments, but permanence has not been established. 176,177Current research focuses on using smaller carbon particles and the laser to propel the carbon into the follicle. Nonlaser Light Source. A nonlaser light source (EpiLight, ESC) that produces incoherent, multiwavelength 2.5 to 7 millisecond pulsed light from 590 to 1200 nm at fluences ranging from 30 to 65 J/cm2 is available. Long wavelengths, long pulse duration, and high fluences should result in follicular damage. With the placement of cutoff filters specific wavebands can be generated. Thus a specific wavelength may be selected to suit the individual's skin type and hair color. When used for hair removal, shorter wavelengths are filtered to maximize the depth of penetration. A coupling gel is applied to the skin surface to prevent excessive epidermal heating and subsequent damage and to increase light penetration into the deeper dermis. Early studies with the Photoderm VL, which was the first available light source of this kind, showed promising results. Fitzpatrick et allTS achieved 62% hair removal after a single treatment with an increased efficacy after multiple treatments. Side effects noted were erythema, epidermal scaling, or blistering in a few patients, but no pigmentary nor textural changes were observed. Photodynamic Therapy. Photodynamic therapy is comprised of a photosensitizer (a light-activated molecule) that is selectively taken by pathologic tissue, a light source whose wavelengths match the absorption

Curr Probl Dermatol, July/August 1998

characteristics of the photosensitizer and oxygen. Aminolevulinic acid is a precursor of porphyrin synthesis that is more selectively absorbed by hair follicles and sebaceous glands than by the epidermis. It is rapidly converted to protoporphyrin IX, a potent photosensitizer by follicular cells. After light exposure protoporphyrin IX is activated, generating singlet oxygen leading to cell membrane damage. A pilot study with topical aminolevulinic acid followed 3 hours later by exposure to 630 nm light from an argon-pumped tunable dye laser showed a dose-dependent reduction in hair regrowth that lasted 6 months beyond treatment. Temporary hyperpigmentation was the only adverse effect noted. 179

Future Directions Laser developments over the last 2 decades have changed the face of dermatology. Within the last decade effective laser treatments for a variety of vascular and pigmented lesions, tattoos, photoaging, and hair removal have all been developed. The future of cutaneous laser surgery is exciting. Several areas of research are in the development of diode technology and in novel approaches to skin rejuvenation. Diode lasers are extremely compact solid state devices with no moving parts, minimal energy requirements, and limited cooling needs. Because they have an extremely long life, being functional for up to 30,000 hours, maintenance costs are low. The wavelength, frequency, and pulse parameters are, to some extent, variable. These advantages are responsible for the recent appearance of diode lasers in the medical marketplace. Most diode lasers emit in the region of 800 nm. An advantage of this wavelength is that it is poorly absorbed by melanin, making it useful in the treatment of vascular lesions. A diode-pumped Nd:YAG laser that delivers 532 nm pulses in the millisecond domain is commercially available for the treatment of facial telangiectasia, and an 805 nm diode has recently been approved for hair removal. Currently, studies are underway to determine diode laser effectiveness in the treatment of leg veins. New approaches to laser resurfacing include attempts at achieving selective dermal injury with the epidermis remaining intact. The healing process in the dermis should lead to new collagen deposition and remodeling, potentially reducing rhytides. A carbon-

167

based topical suspension applied to the skin followed by low-fluence Q-switched Nd:YAG laser irradiation aS° and the use of a mid infrared (1.32 gm) pulsed (0.2 msec) laser 181 to produce dermal shrinkage while the epidermis is protected with dynamic cooling have both demonstrated moderate improvement of rhytides in small pilot studies. Rhytid improvement has also been demonstrated after nonabtative resurfacing with a Q-switched Nd:YAG laser, 182 although larger studies with long-term follow-up are necessary.

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