Safety and efficacy of botulinum toxin type B (Myobloc) in adductor spasmodic dysphonia

This single-site, open-label, dose-finding study evaluated the safety and efficacy of botulinum toxin type B (BoNT-B; Myobloc) for the treatment of adductor spasmodic dysphonia (AdSD) in 13 patients. Three patients received a total of 50 U (25 U per vocal fold); the same three subsequently received 100 U, and then 10 more received 200 U. The primary measure of efficacy was the patient's rating of the change in the severity of spasms on a scale from -3 to +3. There were seven secondary measures of efficacy, including blinded ratings of the sound of voice recorded on audiotape. At Week 8 after injection, spasms improved in 0 of 3 patients who received 50 U, 1 of 3 patients who received 100 U, and 8 of 10 patients who received 200 U. The mean (+/- standard deviation [SD]) score for the change in spasm severity at Week 8 in the 200 U group was 1.4 (+/-1.2) points (P = 0.004). All seven secondary measures also showed improvement. Breathiness was the most common side effect but was mild in intensity and of short duration. We conclude that BoNT-B is safe and effective for the treatment of adductor spasmodic dysphonia. (C) 2004 Movement Disorder Society.