Long-term botulinum toxin treatment of cervical dystonia - EMG changes in injected and noninjected muscles

Objective: To evaluate changes in quantitative EMG of injected and noninjec ted sternocleidomastoid muscles following long-term unilateral botulinum to xin treatment of cervical dystonia. Methods: We investigated 27 patients with cervical dystonia, who received r epeated unilateral botulinum toxin injections of the sternocleidomastoid mu scle, with quantitative EMG at rest and at maximal voluntary contraction. T he patients had on the average 7.1 botulinum toxin treatments and the follo w-up period was on the average 31 months (SD 16). Results: After the first treatment, the injected sternocleidomastoid muscle s showed a significant decrease in turns/s (mean 45%) and amplitude (mean 5 2%) at lest, and in amplitude at maximal flexion (mean 24%) and rotation (m ean 39%). Except for a reduction in turns/s at rotation (mean 19%) no furth er reductions in EMG parameters were seen after long-term treatment. The co ntralateral noninjected sternocleidomastoid muscles showed no significant c hange in EMG activity after the first BT treatment, but after long-term tre atment a significant reduction in turns/s and amplitude at both maximal fle xion (turns: mean 28%; amplitude: mean 25%) and rotation (turns/s: mean 32% ; amplitude: mean 25%) were seen as compared to pretreatment values, Conclusion: The results indicate that there seems to be no cumulative chemo denervation by repeated botulinum toxin injections of sternocleidomastoid m uscles measured by quantitative EMG. Contralateral noninjected stemocleidom astoid muscles however, seem to be affected following long-term treatment. The mechanism behind this finding is unknown. (C) 1999 Elsevier Science Ire land Ltd. All rights reserved.