Quantitative electromyographic analysis of changes in muscle activity following botulinum toxin therapy for cervical dystonia.

Reports of efficacy of botulinum toxin for cervical dystonia have relied on subjective reports of improvement or various clinical rating scales. We studied 19 patients with cervical dystonia using Turns analysis to determine if quantitative EMG measures of muscle activity changed following botulinum toxin injections. Before and after botulinum toxin injections, six muscles were evaluated bilaterally. Quantitative EMG analysis of active muscles injected with botulinum toxin showed a significant decline in muscle activity after botulinum toxin (F = [1,41] 55.0; p < 0.001). Significant reductions in quantitative EMG parameters were also noted in noninjected active muscles after botulinum toxin treatment (F = [1,51] 59.15; p < 0.001). The sum of EMG activity for all active muscles was calculated for each subject and showed a significant reduction after botulinum toxin injection [MANOVA: (F = [1,5] 5.69; p < 0.05]. Quantitative EMG assessment provides an objective measure of response to botulinum toxin. Decreased muscle activity in noninjected muscles may result from toxin diffusion or reflect relaxation of muscles only secondarily involved in cervical dystonia.