Botulinum Toxin in Secondarily Nonresponsive Patients with Spasmodic Dysphonia.

Chemodenervation with botulinum toxin (BoNT) has been effective and well tolerated for all types of dystonia for >30 years. We reviewed outcomes of our patients treated with BoNT serotype A (BoNT-A) for spasmodic dysphonia (SD) who became secondarily nonresponsive. We found that 8 of 1400 patients became nonresponsive to BoNT-A (0.57%), which is lower than the secondary nonresponse rate in other dystonias. After a cessation period, 4 of our patients resumed BoNT-A injections, and recurrence of immunoresistance was not seen in any of them. When compared with patients with other dystonias, patients with SD receive extremely low doses of BoNT. Small antigen challenge may explain the lower rate of immunoresistance and long-lasting efficacy after BoNT-A is restarted among secondary nonresponsive patients with SD.