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Rest azured?
874 Letters
J AM ACAD DERMATOL MAY 2001
color. To whom the concept of color contrast in skin would be helpful I cannot say. But I hope it will assist those who seek a more complete and satisfying explanation of what we perceive. Peter L. Reisfeld, MD Department of Dermatology New York University Medical Center State University of New York at Stoney Brook 4100 Duff Place Seaford, NY 11783 REFERENCES 1. Jameson D, Hurvich LM.Theory of brightness and color contrast in human vision. Vision Res 1964;4:135-54. 2. Reisfeld PL. Blue in the skin. J Am Acad Dermatol 2000;42:595605. 3. Committee on Colorimetry, Optical Society of America. The science of color. New York: Thomas Y Crowell Co; 1953. p. 41. 4. Monash S. Skin color. Arch Dermatol 1961;84:654-9. 16/8/112921 doi:10.1067/mjd.2001.112921
Rest azured? To the Editor: Dr Bernhard shared with me the colorful, contrasting letters from Drs Smith and Reisfeld, each raising excellent points of view. Lest readers of The Blue Journal turn the same color, I feel compelled to respond. In medical school, I got the notion that laser pulses could specifically affect blood vessels in the skin (eg, the venules of port-wine stains). Delving into this led to the wonderful academic hobby of skin optics. In the 20 years since, hundreds of optical spectra of skin, skin layers, and skin components have been measured; new journals have sprung up devoted to tissue optics; powerful computers allowed us to model the complex optics of skin. However, all this progress hasn’t really helped us much to understand the exact skin colors we see. Color is, by definition, a perception, which means it depends on both a physical stimulus (light) and a mental process. We humans are, in general, lousy spectrophotometers. We aren’t very quantitative, and we only perceive a little slice of the electromagnetic system. However, spectrophotometers and even the latest digital hyperspectral imaging technology from the National Aeronautics and Space Administration don’t “see” nearly as well as we do. I’ve had fun with this tug-of-war for many years and wrote a little piece on blue skin apparently missed by Reisfeld (Anderson RR, “The Physical Basis of ‘Blue’ Skin Color,” in Biology and Diseases of Dermal Pigmentation, Tokyo, 1981, University of Tokyo Press, p. 5-6). Dare I suggest that both Smith and Reisfeld are correct? Yes!
Reisfeld has shown us that the color of skin veins is influenced by the perceptual phenomenon of color contrast, in which the veins appear bluish only in contrast to the surrounding pinkish skin. Indeed, a gray (neutral reflectance spectrum) object will appear bluish when placed on a reddish background, and vice versa. But this is only part of the story. Physically, what is responsible for attenuating the reflectance of red light from skin where a vein is located? Reisfeld doesn’t really say. Smith has the answer—absorption by deoxyhemoglobin—although he focuses on the wrong part of deoxyhemoglobin’s absorption spectrum. With respect to influencing skin color, it makes little difference that oxyhemoglobin and deoxyhemoglobin have slightly different absorption bands in the blue, green, and yellow wavelengths (400-600 nm). At their actual concentrations in blood, either of these hemoglobins renders essentially all vein lumens to be opaque at these wavelengths. The answer lies in the giant, order-of-magnitude greater absorption by deoxyhemoglobin relative to oxyhemoglobin, in the red wavelengths from about 620 to 700 nm. Arterioles and small arteries barely absorb any red light; veins larger than approximately 0.3 mm in diameter absorb most of the red light that encounters them. In normal dermis, veins and pigmented hair follicles are the only structures that absorb much red light (note that the male beard “5 o’clock shadow” is also bluish). Reisfeld downplays the importance of adding even a little bit of red light absorption to a dermis that otherwise has almost none. This really has a large effect on skin color, which for veins and some local skin lesions is further enhanced by color contrast perception. Smith asks brilliantly, What about the cyanosis of hypoxia or methemoglobinemia or the bright pinkness of carbon monoxide poisoning? Color contrast perception simply cannot explain these total-body hues. What does? Absorption of red light in the dermis! Carboxyhemoglobin (HbCO) absorbs even less red light than oxyhemoglobin (HBO2); unlike O2, CO is not released in the capillaries, such that the venous blood contains less deoxyhemoglobin. Both of these factors make the skin look pinker or redder. Methemoglobin, which is unable to bind a gas ligand, absorbs red light even more than deoxyhemoglobin; therefore cyanosis can occur with relatively low methemoglobin levels. So, are our veins really gray, even though we see them as bluish? I say no, because color is defined by how we perceptually label it. We are the only umpires in the color game. The perceptual phenomenon known as color contrast is a factor when we assign color to veins, but just as surely, the skin can be downright blue. There are no blue pigments in
Letters 875
J AM ACAD DERMATOL VOLUME 44, NUMBER 5
skin, or in the iris of the most gorgeous blue eyes. What makes us truly blue, or just a little bluish here and there, is the combination of (1) stronger optical scattering by dermal collagen at shorter wavelengths and (2) the presence of anything in the dermis that substantially absorbs red light. R. Rox Anderson, MD Massachusetts General Hospital Boston, Massachusetts 16/8/112922 doi:10.1067/mjd.2001.112922
Fig 1. Subungual melanoma with extension onto hyponychium.
Subungual melanoma obscured by nail polish To the Editor: We read with great interest the article by Levit et al,1 which described 6 criteria for diagnosing subungual melanoma summarized by the letters ABCDEF. The E stands for extension of the brown or black pigment to involve the proximal or lateral nailfold (Hutchinson’s sign) or free edge of the nail plate.1,2 We report a case presenting with extension of pigment from the nailbed onto the hyponychium of the thumb in a patient who grew long fingernails and wore colored nail polish obscuring the nail plate. A 54-year-old black woman had discoloration on her right thumbnail and hyponychium of 2 years’ duration. Thirty years earlier, she had initially noticed a longitudinal pigmented streak in the nail, which gradually spread over time. As she had always worn nail polish, she was not concerned about the appearance of the affected thumbnail nor was it noted by any physicians. On initial examination, she had an irregularly defined 8-mm black pigmented macule on the distal right thumb. The pigment was only visible by examining the volar skin under the free edge of her thumbnail because all of her nails including the affected thumbnail were entirely covered with colored nail polish. The nail plate was intact. Pigment extension onto the proximal or lateral nailfold was not seen. She was asked to remove the nail polish revealing black pigmentation of the entire nail plate. The nail plate was intact and not dystrophic (Fig 1). The nail plate was avulsed. A punch biopsy specimen from the nail bed showed a proliferation of single melanocytes at the dermoepidermal junction and slightly above it. Numerous melanophages were seen. A punch biopsy specimen from the volar skin at the distal nailfold showed acral skin with a proliferation of atypical melanocytes arranged predominantly as single cells and irregular nests at the dermoepidermal junction and above it, consistent with the diagnosis of melanoma in situ. A wide and deep excision of the distal thumb with skin grafting
showed a very similar histologic picture to the punch biopsy specimens, which confirmed a diagnosis of malignant melanoma, predominantly in situ, with focal invasion of the nail bed, thickness of approximately 0.42 mm. The lesion extended from the nail matrix distally to the volar skin of the thumb. Mitotic figures were absent. No evidence of spread was noted at the time of surgery. Extension of pigment onto the volar skin from the nail bed was useful to make a diagnosis of subungual melanoma in the patient. In patients whose nail plates are obscured by nail enamel, early diagnosis of subungual melanoma may be delayed. It may be impractical to ask all patients seen in a dermatology office to remove their nail polish for the purpose of a complete skin examination unless that is their presenting complaint. We submit that the extension of pigment onto the hyponychium from the nail bed should be included as a criterion for the diagnosis of subungual melanoma. Barry D. Goldman, MDa Phoebe Rich, MDb New York University Medical Center New York, New Yorka Oregon Health Sciences University Portland, Oregonb REFERENCES 1. Levit EK, Kagen MH, Scher RK, Grossman M, Altman E. The ABC rule for subclinical detection of subungual melanoma. J Am Acad Dermatol 2000;42:269-74. 2. Baran R, Kechijian P. Hutchinson’s sign: a reappraisal. J Am Acad Dermatol 1996;34:87-90. 16/8/113684 doi:10.1067/mjd.2001.113684
Muckle-Wells syndrome? To the Editor: We read with great interest the brief communication by Lieberman, Grossman, and Silvers
J AM ACAD DERMATOL MAY 2001
color. To whom the concept of color contrast in skin would be helpful I cannot say. But I hope it will assist those who seek a more complete and satisfying explanation of what we perceive. Peter L. Reisfeld, MD Department of Dermatology New York University Medical Center State University of New York at Stoney Brook 4100 Duff Place Seaford, NY 11783 REFERENCES 1. Jameson D, Hurvich LM.Theory of brightness and color contrast in human vision. Vision Res 1964;4:135-54. 2. Reisfeld PL. Blue in the skin. J Am Acad Dermatol 2000;42:595605. 3. Committee on Colorimetry, Optical Society of America. The science of color. New York: Thomas Y Crowell Co; 1953. p. 41. 4. Monash S. Skin color. Arch Dermatol 1961;84:654-9. 16/8/112921 doi:10.1067/mjd.2001.112921
Rest azured? To the Editor: Dr Bernhard shared with me the colorful, contrasting letters from Drs Smith and Reisfeld, each raising excellent points of view. Lest readers of The Blue Journal turn the same color, I feel compelled to respond. In medical school, I got the notion that laser pulses could specifically affect blood vessels in the skin (eg, the venules of port-wine stains). Delving into this led to the wonderful academic hobby of skin optics. In the 20 years since, hundreds of optical spectra of skin, skin layers, and skin components have been measured; new journals have sprung up devoted to tissue optics; powerful computers allowed us to model the complex optics of skin. However, all this progress hasn’t really helped us much to understand the exact skin colors we see. Color is, by definition, a perception, which means it depends on both a physical stimulus (light) and a mental process. We humans are, in general, lousy spectrophotometers. We aren’t very quantitative, and we only perceive a little slice of the electromagnetic system. However, spectrophotometers and even the latest digital hyperspectral imaging technology from the National Aeronautics and Space Administration don’t “see” nearly as well as we do. I’ve had fun with this tug-of-war for many years and wrote a little piece on blue skin apparently missed by Reisfeld (Anderson RR, “The Physical Basis of ‘Blue’ Skin Color,” in Biology and Diseases of Dermal Pigmentation, Tokyo, 1981, University of Tokyo Press, p. 5-6). Dare I suggest that both Smith and Reisfeld are correct? Yes!
Reisfeld has shown us that the color of skin veins is influenced by the perceptual phenomenon of color contrast, in which the veins appear bluish only in contrast to the surrounding pinkish skin. Indeed, a gray (neutral reflectance spectrum) object will appear bluish when placed on a reddish background, and vice versa. But this is only part of the story. Physically, what is responsible for attenuating the reflectance of red light from skin where a vein is located? Reisfeld doesn’t really say. Smith has the answer—absorption by deoxyhemoglobin—although he focuses on the wrong part of deoxyhemoglobin’s absorption spectrum. With respect to influencing skin color, it makes little difference that oxyhemoglobin and deoxyhemoglobin have slightly different absorption bands in the blue, green, and yellow wavelengths (400-600 nm). At their actual concentrations in blood, either of these hemoglobins renders essentially all vein lumens to be opaque at these wavelengths. The answer lies in the giant, order-of-magnitude greater absorption by deoxyhemoglobin relative to oxyhemoglobin, in the red wavelengths from about 620 to 700 nm. Arterioles and small arteries barely absorb any red light; veins larger than approximately 0.3 mm in diameter absorb most of the red light that encounters them. In normal dermis, veins and pigmented hair follicles are the only structures that absorb much red light (note that the male beard “5 o’clock shadow” is also bluish). Reisfeld downplays the importance of adding even a little bit of red light absorption to a dermis that otherwise has almost none. This really has a large effect on skin color, which for veins and some local skin lesions is further enhanced by color contrast perception. Smith asks brilliantly, What about the cyanosis of hypoxia or methemoglobinemia or the bright pinkness of carbon monoxide poisoning? Color contrast perception simply cannot explain these total-body hues. What does? Absorption of red light in the dermis! Carboxyhemoglobin (HbCO) absorbs even less red light than oxyhemoglobin (HBO2); unlike O2, CO is not released in the capillaries, such that the venous blood contains less deoxyhemoglobin. Both of these factors make the skin look pinker or redder. Methemoglobin, which is unable to bind a gas ligand, absorbs red light even more than deoxyhemoglobin; therefore cyanosis can occur with relatively low methemoglobin levels. So, are our veins really gray, even though we see them as bluish? I say no, because color is defined by how we perceptually label it. We are the only umpires in the color game. The perceptual phenomenon known as color contrast is a factor when we assign color to veins, but just as surely, the skin can be downright blue. There are no blue pigments in
Letters 875
J AM ACAD DERMATOL VOLUME 44, NUMBER 5
skin, or in the iris of the most gorgeous blue eyes. What makes us truly blue, or just a little bluish here and there, is the combination of (1) stronger optical scattering by dermal collagen at shorter wavelengths and (2) the presence of anything in the dermis that substantially absorbs red light. R. Rox Anderson, MD Massachusetts General Hospital Boston, Massachusetts 16/8/112922 doi:10.1067/mjd.2001.112922
Fig 1. Subungual melanoma with extension onto hyponychium.
Subungual melanoma obscured by nail polish To the Editor: We read with great interest the article by Levit et al,1 which described 6 criteria for diagnosing subungual melanoma summarized by the letters ABCDEF. The E stands for extension of the brown or black pigment to involve the proximal or lateral nailfold (Hutchinson’s sign) or free edge of the nail plate.1,2 We report a case presenting with extension of pigment from the nailbed onto the hyponychium of the thumb in a patient who grew long fingernails and wore colored nail polish obscuring the nail plate. A 54-year-old black woman had discoloration on her right thumbnail and hyponychium of 2 years’ duration. Thirty years earlier, she had initially noticed a longitudinal pigmented streak in the nail, which gradually spread over time. As she had always worn nail polish, she was not concerned about the appearance of the affected thumbnail nor was it noted by any physicians. On initial examination, she had an irregularly defined 8-mm black pigmented macule on the distal right thumb. The pigment was only visible by examining the volar skin under the free edge of her thumbnail because all of her nails including the affected thumbnail were entirely covered with colored nail polish. The nail plate was intact. Pigment extension onto the proximal or lateral nailfold was not seen. She was asked to remove the nail polish revealing black pigmentation of the entire nail plate. The nail plate was intact and not dystrophic (Fig 1). The nail plate was avulsed. A punch biopsy specimen from the nail bed showed a proliferation of single melanocytes at the dermoepidermal junction and slightly above it. Numerous melanophages were seen. A punch biopsy specimen from the volar skin at the distal nailfold showed acral skin with a proliferation of atypical melanocytes arranged predominantly as single cells and irregular nests at the dermoepidermal junction and above it, consistent with the diagnosis of melanoma in situ. A wide and deep excision of the distal thumb with skin grafting
showed a very similar histologic picture to the punch biopsy specimens, which confirmed a diagnosis of malignant melanoma, predominantly in situ, with focal invasion of the nail bed, thickness of approximately 0.42 mm. The lesion extended from the nail matrix distally to the volar skin of the thumb. Mitotic figures were absent. No evidence of spread was noted at the time of surgery. Extension of pigment onto the volar skin from the nail bed was useful to make a diagnosis of subungual melanoma in the patient. In patients whose nail plates are obscured by nail enamel, early diagnosis of subungual melanoma may be delayed. It may be impractical to ask all patients seen in a dermatology office to remove their nail polish for the purpose of a complete skin examination unless that is their presenting complaint. We submit that the extension of pigment onto the hyponychium from the nail bed should be included as a criterion for the diagnosis of subungual melanoma. Barry D. Goldman, MDa Phoebe Rich, MDb New York University Medical Center New York, New Yorka Oregon Health Sciences University Portland, Oregonb REFERENCES 1. Levit EK, Kagen MH, Scher RK, Grossman M, Altman E. The ABC rule for subclinical detection of subungual melanoma. J Am Acad Dermatol 2000;42:269-74. 2. Baran R, Kechijian P. Hutchinson’s sign: a reappraisal. J Am Acad Dermatol 1996;34:87-90. 16/8/113684 doi:10.1067/mjd.2001.113684
Muckle-Wells syndrome? To the Editor: We read with great interest the brief communication by Lieberman, Grossman, and Silvers