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Vocal tract response to toxic injury: Clinical issues
Journal of Voice
Vol. 8, No. 1, pp. 63--64 © 1994 Raven Press, Lfd., New York
Vocal Tract Response to Toxic Injury: Clinical Issues Robert Thayer Sataloff Department of Otolaryngology, Thomas Jefferson University, Philadelphia, Pennsylvania, U.S.A.
Summary: Toxic substances commonly affect the voice. In many cases, the mechanism of toxicity is unknown. Treatment is often based on intuition, rather than scientific fact. Extensive collaborative research is needed. Key Words: Voice--Toxicity--Neurolaryngology.
Toxic substances are ubiquitous. We find them in the home, workplace, air, food chain, and even in the medical treatment room. For generations, physicians have endeavored to understand and control toxic substances to prevent bodily injuries. Many substances are toxic to the vocal tract, although few are fully understood. In addition, medical science has routinely taken advantage of toxic substances, controlling them for therapeutic advantage. For exampl e , the vestibular toxicity of systemic streptomycin is used to treat dizziness in selected patients with bilateral labyrinthine dysfunction. Many chemotherapeutic agents used for cancer are toxic, but they are used in doses and combinations that optimize injury to cancer cells while minimizing injury to healthy cells. In keeping with this therapeutic tradition, in the last several years voice specialists have taken advantage of the toxic effects of botulih u m toxin to treat patients with spasmodic dysphonia and other conditions that impair voice and speech. Clinical questions regarding neurolaryngologic response to toxic injury may be divided into two categories: inadvertent injury and therapeutic injury. Inadvertent toxic injury to the vocal tract is not rare. Inhalant injuries are most obvious. Such problems are usually seen following fires or industrial accidents in which hydrocarbons or other sub-
stances are inhaled, and pulmonary and laryngeal dysfunction ensue. Some inhaled toxic substances are absorbed into the body and remain there for prolonged periods of time causing delayed damage due to body response, as seen with asbestosis, silicosis, berylliosis, and other pneumoconioses. In other cases, the insult appears to be topical. In both scenarios, the consequent voice dysfunction is often more severe and prolonged than one would expect, even when there is no secondary gain (such as litigation) that might confuse the picture. The mechanism of these problems remains obscure. Indeed, it is unclear even whether such conditions result from injury to nerves, control mechanisms, surface integrity, other factors, or combinations of such mechanisms. To accurately diagnose and treat such problems, and to predict their long-term course, we need a much better understanding of the effects of inhalant toxins on the vocal tract, and on its neurological components, in particular. In addition to inhaled toxins, physicians are commonly confronted with ingested substances that may adversely affect voice function through toxicity, and may alter neurological function. Such substances include not only widely recognized neurotoxins (such as lead), but possibly also more common substances, including alcohol, caffeine, and various drugs (prescribed and recreational). Optimal vocal health is dependent on fine motor control. In fact, much of professional voice training is devoted to developing sophisticated neuromuscular coordination. Very little is known about the effects of many commonly ingested chemicals on the
Accepted August 3, 1992. Address correspondence and reprint requests to Dr. R. Thayer Sataloff at The Voice Foundation, 1721 Pine Street, Philadelphia, PA 19103, U.S.A.
63
64
R. T H A Y E R S A T A L O F F
neurological component of the vocal tract. Naturally, environmental toxins can be absorbed in other ways, such as through the skin. Even noise intense enough to cause hearing loss and interfere with auditory feedback used for voice control might be considered a neurolaryngologic toxin, in the broader sense. That is, it has been generally recognized for decades that sensorineural hearing impairment may be accompanied by voice abnormalities, particularly excessive volume that can produce voice fatigue, hoarseness, and nodules. Diagnostic mysteries such as spasmodic dysphonia raise other questions about possible toxic or traumatic factors affecting neurological function or control. These subjects are beyond the scope of this brief review, but a great deal of clinically useful information remains to be discovered through research on neurotoxicity and voice. Issues of therapeutic toxicity for treatment of voice disorders currently center around botulinum toxin. Although this substance is most prominent for its use in treatment of adductor spasmodic dysphonia, it is also under investigation for management of other voice disorders, including abductor spasmodic dysphonia, tremor, and stuttering (1). Botulinum toxin is used widely for treatment of dystonias elsewhere in the body (2,3). Nevertheless, many troubling questions remain. We do not fully understand the drug's mechanism of action or me-
Journal of Voice, Vol. 8, No. 1, 1994
tabolism, the body's mechanism of recovery from injury, the nature and development of immune response, reasons for response failures, methods to minimize dosage and maximize effect, and many other phenomena. Moreover, we are not at all certain whether the serotype in current use is the best choice, or even whether clostridial toxins are the most appropriate to use for spasmodic dysphonia and the other conditions being treated. These knowledge gaps, coupled with rapidly expanding clinical use, highlight the need for expeditious, expert research. Toxic injuries are seen routinely in otolaryngologic practice. Because the mechanisms through which toxins exert their effects on neuromuscular and other functions are not fully understood, clinical diagnosis and treatment must often be guided by intuition, imagination and anecdote. To improve this uneasy situation, extensive collaborative research is essential. REFERENCES 1. Ludlow CL. Clinical trials for speech disorders. Presented at the NIH Consensus Development Conference on clinical use of botulinum toxin, Bethesda, Maryland, November 13, 1990. 2. Jankovic J, Brin MF. Therapeutic uses of botulinum toxin. N Engl J M e d 1991 ;324:1186-94. 3. National Institute of Health Consensus Development Panel on clinical use of botulinum toxin. J Voice 1992;6:394-400.
Vol. 8, No. 1, pp. 63--64 © 1994 Raven Press, Lfd., New York
Vocal Tract Response to Toxic Injury: Clinical Issues Robert Thayer Sataloff Department of Otolaryngology, Thomas Jefferson University, Philadelphia, Pennsylvania, U.S.A.
Summary: Toxic substances commonly affect the voice. In many cases, the mechanism of toxicity is unknown. Treatment is often based on intuition, rather than scientific fact. Extensive collaborative research is needed. Key Words: Voice--Toxicity--Neurolaryngology.
Toxic substances are ubiquitous. We find them in the home, workplace, air, food chain, and even in the medical treatment room. For generations, physicians have endeavored to understand and control toxic substances to prevent bodily injuries. Many substances are toxic to the vocal tract, although few are fully understood. In addition, medical science has routinely taken advantage of toxic substances, controlling them for therapeutic advantage. For exampl e , the vestibular toxicity of systemic streptomycin is used to treat dizziness in selected patients with bilateral labyrinthine dysfunction. Many chemotherapeutic agents used for cancer are toxic, but they are used in doses and combinations that optimize injury to cancer cells while minimizing injury to healthy cells. In keeping with this therapeutic tradition, in the last several years voice specialists have taken advantage of the toxic effects of botulih u m toxin to treat patients with spasmodic dysphonia and other conditions that impair voice and speech. Clinical questions regarding neurolaryngologic response to toxic injury may be divided into two categories: inadvertent injury and therapeutic injury. Inadvertent toxic injury to the vocal tract is not rare. Inhalant injuries are most obvious. Such problems are usually seen following fires or industrial accidents in which hydrocarbons or other sub-
stances are inhaled, and pulmonary and laryngeal dysfunction ensue. Some inhaled toxic substances are absorbed into the body and remain there for prolonged periods of time causing delayed damage due to body response, as seen with asbestosis, silicosis, berylliosis, and other pneumoconioses. In other cases, the insult appears to be topical. In both scenarios, the consequent voice dysfunction is often more severe and prolonged than one would expect, even when there is no secondary gain (such as litigation) that might confuse the picture. The mechanism of these problems remains obscure. Indeed, it is unclear even whether such conditions result from injury to nerves, control mechanisms, surface integrity, other factors, or combinations of such mechanisms. To accurately diagnose and treat such problems, and to predict their long-term course, we need a much better understanding of the effects of inhalant toxins on the vocal tract, and on its neurological components, in particular. In addition to inhaled toxins, physicians are commonly confronted with ingested substances that may adversely affect voice function through toxicity, and may alter neurological function. Such substances include not only widely recognized neurotoxins (such as lead), but possibly also more common substances, including alcohol, caffeine, and various drugs (prescribed and recreational). Optimal vocal health is dependent on fine motor control. In fact, much of professional voice training is devoted to developing sophisticated neuromuscular coordination. Very little is known about the effects of many commonly ingested chemicals on the
Accepted August 3, 1992. Address correspondence and reprint requests to Dr. R. Thayer Sataloff at The Voice Foundation, 1721 Pine Street, Philadelphia, PA 19103, U.S.A.
63
64
R. T H A Y E R S A T A L O F F
neurological component of the vocal tract. Naturally, environmental toxins can be absorbed in other ways, such as through the skin. Even noise intense enough to cause hearing loss and interfere with auditory feedback used for voice control might be considered a neurolaryngologic toxin, in the broader sense. That is, it has been generally recognized for decades that sensorineural hearing impairment may be accompanied by voice abnormalities, particularly excessive volume that can produce voice fatigue, hoarseness, and nodules. Diagnostic mysteries such as spasmodic dysphonia raise other questions about possible toxic or traumatic factors affecting neurological function or control. These subjects are beyond the scope of this brief review, but a great deal of clinically useful information remains to be discovered through research on neurotoxicity and voice. Issues of therapeutic toxicity for treatment of voice disorders currently center around botulinum toxin. Although this substance is most prominent for its use in treatment of adductor spasmodic dysphonia, it is also under investigation for management of other voice disorders, including abductor spasmodic dysphonia, tremor, and stuttering (1). Botulinum toxin is used widely for treatment of dystonias elsewhere in the body (2,3). Nevertheless, many troubling questions remain. We do not fully understand the drug's mechanism of action or me-
Journal of Voice, Vol. 8, No. 1, 1994
tabolism, the body's mechanism of recovery from injury, the nature and development of immune response, reasons for response failures, methods to minimize dosage and maximize effect, and many other phenomena. Moreover, we are not at all certain whether the serotype in current use is the best choice, or even whether clostridial toxins are the most appropriate to use for spasmodic dysphonia and the other conditions being treated. These knowledge gaps, coupled with rapidly expanding clinical use, highlight the need for expeditious, expert research. Toxic injuries are seen routinely in otolaryngologic practice. Because the mechanisms through which toxins exert their effects on neuromuscular and other functions are not fully understood, clinical diagnosis and treatment must often be guided by intuition, imagination and anecdote. To improve this uneasy situation, extensive collaborative research is essential. REFERENCES 1. Ludlow CL. Clinical trials for speech disorders. Presented at the NIH Consensus Development Conference on clinical use of botulinum toxin, Bethesda, Maryland, November 13, 1990. 2. Jankovic J, Brin MF. Therapeutic uses of botulinum toxin. N Engl J M e d 1991 ;324:1186-94. 3. National Institute of Health Consensus Development Panel on clinical use of botulinum toxin. J Voice 1992;6:394-400.