Dextromethorphan to Treat Patients With Voice Spasms

Studies of spasmodic dysphonia (SD) have increasingly pointed to the possibility of a central sensori-motor control disorder. Sensori-motor processing has been found abnormal in both adductor and abductor spasmodic dysphonia based on reflex conditioning studies. These studies demonstrated an increased frequency of R2 muscle responses during rapid paired presentation of electrical stimuli to the superior laryngeal nerve in spasmodic dysphonia. Thus, uncontrolled R2 responses were hypothesized to be the basis for the uncontrolled muscle bursts in these patients. Selective suppression of late R2 laryngeal adductor responses by N-methyl-D-Aspartate (NMDA) blockade in cats was demonstrated by Ambalavanar et.al. In particular, dextromethorphan reduced the frequency of R2 responses from 95% to 25% (P = 0.015). Dextromethorphan is a widely used antitussive agent that has been in use for over 30 years. In a double-blind randomized crossover design, 3 groups of patients will receive be randomly assigned to one of 6 order cohorts. They will then receive either dextromethorphan at a 8 mg/kg/d dose divided in a Q6 hour dosing schedule with only 3 doses administered PO every 6 hours for 3 dosages, 04 mg/kg/d of lorazepam PO every 6 hours for 3 dosages or a placebo administrated in the same way during Phase A. After a minimum of a 1-week washout interval, the patients will be given either the other medication or placebo during Phase B and then the remaining medication or placebo during Phase C. Our hypothesis is that dextromethorphan, an NMDA receptor blocker, will reduce voice breaks in spasmodic dysphonia to a greater degree than lorazepam, which has similar sedating side effects, but does not affect NMDA receptors with a different mechanism. On the other hand, patients with other idiopathic voice disorders, muscular tension dysphonia and vocal tremor, are hypothesized not to have a similar benefit from dextromethorphan. During the double-blind randomized cross-over study, three groups will be included, 10 patients with adductor or abductor spasmodic dysphonia, 10 with muscular tension dysphonia and 10 with vocal tremor. The results will determine if dextromethorphan has potential as a treatment option for patients with adductor or abductor SD.