With paresis of both vocal cords, the patient can speak only in whispers. Because the vocal cords normally separate during inspiration, their failure to do so when paralyzed may result in an inspiratory stridor. If one vocal cord is paralyzed as a result of involvement of the tenth cranial nerve by tumor, for example, the voice becomes hoarse, low-pitched, rasping, and somewhat nasal in quality. The pronunciation of certain consonants such as b, p, n, and k is followed by an escape of air into the nasal passages. The abnormality is sometimes less pronounced in recumbency and increased when the head is thrown forward. Prolonged tracheal intubation that causes pressure necrosis of the posterior cricoarytenoid cartilage and the underlying posterior branch of the laryngeal nerve is an increasingly common iatrogenic cause.
Various tremor disorders, but especially severe essential tremor, affect the voice by creating an oscillatory effect on the vocal cords (see Chap. 4 for a full discussion). An unusual form of this disease causes a vibrato voice tremor almost in isolation, but most cases occur in the context of severe generalized essential tremor. As noted below, the pitch of voice may increase and simulate spasmodic dysphonia. Only the most severe cases of Parkinson tremor impart a warbling to the voice but this appears to be from vibration of the body and chest.
This is a relatively common condition about which little is known. Spasmodic dysphonia is a better term than the still-appearing spastic dysphonia, as the adjective spastic suggests corticospinal involvement, whereas the disorder is probably of extrapyramidal origin. The authors, like most neurologists, have seen many patients, middle-aged or elderly men and women, otherwise healthy, who lose the ability to speak quietly and fluently. Any attempt to speak results in simultaneous contraction of the speech musculature, so that the patient’s voice is strained and speaking requires an effort. The patient sounds as though he were trying to speak while being strangled. Shouting is easier than quiet speech, and whispering is unaltered. Other actions utilizing approximately the same muscles (swallowing and singing) are usually unimpeded.
Spasmodic dysphonia is usually relatively nonprogressive and occurs as an isolated phenomenon, but we have observed exceptions in which it occurs in various combinations with blepharospasm, spasmodic torticollis, writer’s cramp, or some other type of segmental dystonia. The nature of spasmodic dysphonia is unclear. As a neurologic disorder, it may be akin to writer’s cramp, that is, a restricted dystonia (see Chap. 6). As mentioned just above, we have at times had difficulty differentiating a severe essential tremor of voice from spasmodic dysphonia. They may even coexist (fortunately, the treatments are similar). An anatomic basis for the condition has not been demonstrated, but careful neuropathologic studies have not been made.
Glottic spasm, as in tetanus, tetany, and certain hereditary metabolic diseases, results in crowing, stridulous phonation.