Multichannel Electromyographic Mapping to Optimize OnabotulinumtoxinA Efficacy in Cervical Dystonia

BACKGROUND Cervical dystonia (CD) is characterized by sustained, involuntary contraction of head and neck muscles. Botulinum toxin injections are established as safe and effective, but unfortunately 15-25% of patients fail to respond. The aim of this study was to examine whether multichannel electromyogaphic mapping improved outcomes in a cohort of antibody-negative onabotulinumtoxinA non-responders by more precisely identifying which muscles were involved in the dystonia. METHODS Patients with cervical dystonia who had "failed chemodenervation therapy" administered by an outside provider were enrolled in a single-blind, randomized, crossover design study. Patients received either a multichannel electromyographic mapping study prior to the first botulinum toxin injection, which was followed by use of only a single-lead injection 16 weeks later (injected by an alternate and blinded movement disorders specialist) or vice versa. The primary outcome measure was change in total Toronto Western Spasmodic Torticollis Rating Scale score 4 weeks after each injection compared with each pre-injection baseline score. RESULTS Nine subjects completed this study. Mean percentage improvement in Total Toronto Western Spasmodic Torticollis Rating Scale was 23.5% using multichannel electromyography compared with 9% using the single-channel technique (p = 0.11). DISCUSSION This pilot study suggests that multichannel electromyographic mapping may result in improved efficacy in the treatment of antibody-negative onabotulinumtoxinA refractory CD.