Resistance to botulinum toxin injections for spasmodic dysphonia

A known complication of botulinum toxin injections in the treatment of dyst onia has been the occasional development of resistance. This has been seen primarily with patients who receive injections for torticollis. We report o n 2 patients who, after several years of receiving injections for spasmodic dysphonia, developed clinical resistance: by failing to have expected voic e improvement after receiving laryngeal reinjection. One of the 2 patients demonstrated antibodies to botulinum toxin by mouse neutralization bioassay . The second patient had negative bioassay results but had no clinical resp onse to the test toxin injection of facial muscles. These cases demonstrate that, although uncommon, resistance to botulinum toxin injections can occu r in the treatment of spasmodic dysphonia. We offer suggestions to limit th is complication.