ELECTROMYOGRAPHY IN CERVICAL DYSTONIA - CHANGES AFTER BOTULINUM AND TRIHEXYPHENIDYL

Background: The value of physical examination in detecting involved ne ck muscles in cervical dystonia (CD) is uncertain and little is known about changes in electromyographic (EMG) features after botulinum toxi n type A (BTA) treatment. Methods: In a double-blind, randomized study we recorded the EMG activities of 420 neck muscles in 42 patients wit h CD before and after treatment with BTA or trihexyphenidyl. We regard ed any needle EMG activity higher than 100 mu V as the gold standard f or involuntary involvement of a muscle in the dystonic posture and com pared this with the results of physical examination. We calculated EMG total scores by adding the scores of the individual muscles. Results: Physical examination had a low predictive value in the detection of i nvolved muscles. There was a significant correlation between changes i n EMG total scores and changes in clinical measurements. We observed i ncreased EMG activity in 20% of noninjected muscles after BTA treatmen t and in 27% of noninjected muscles after trihexyphenidyl treatment. A switch from one most active muscle to another was seen equally in bot h groups and had no influence on clinical response. Conclusion: Physic al examination alone is not sufficient to detect involved muscles, and repeated, simultaneous EMG-guided application of BTA may be helpful. In addition to clinical measurements, changes in EMG activity due to t reatment can be used as a physiologic measure in evaluating treatment response. Increased activity of noninjected muscles and a switch from one most active muscle to another are not related to BTA treatment, bu t are probably pathophysiologic phenomena of CD itself.