Neuropathology of spasmodic dysphonia.

Spasmodic dysphonia is a devastating voice disorder of unknown etiology, with a variable clinical presentation and response to treatment. Three independent evaluations of brain stem function were performed on spasmodic dysphonic patients, and age and sex-matched controls. Statistically significant (p less than 0.01 approximately 0.05) differences were noted between these groups, and the findings were consistent with impairment of somatic and visceral brain stem pathways. A significant correlation (p less than 0.05) was found between the severity of tested central nervous system impairment and vocal tremor, number of associated neurologic signs and duration of illness. Possible etiologies (viral or traumatic), age, and sex, did not correlate with the severity of brain stem impairment. Clinical signs and the brain stem findings appeared to stabilize 3 to 5 years after onset of dysphonia. The investigation of other spasmodic cranial nerve disorders afforded insight into the etiology and therapy for spasmodic dysphonia. Drawing upon previous observations and the results of the brain stem tests, two models are proposed for neuronal processing in spasmodic dysphonia, and future strategies are discussed. The evidence cited in this research project are consistent with spasmodic dysphonia being one of several spasmodic brain stem disorders with variable presentation which are known by the cranial nerve nuclei or pathways of major clinical involvement.