DOES ULNAR NEUROPATHY PREDISPOSE TO FOCAL DYSTONIA

We have observed a high incidence of ulnar neuropathy in musicians wit h dystonic flexion of the ipsilateral little and ring fingers. To inve stigate the relationship between ulnar neuropathy and focal dystonia, we compared the patterns of surface EMG activity in extensor digitorum communis (EDC4) and flexor digitorum superficialis (FDS4) during tapp ing of the ring finger in normal controls and patients with ulnar neur opathy or focal dystonia. Ten of 10 normal subjects exhibited well-for med alternating EMG bursts in EDC4 and FDS4 separated by clear silent periods. Seven of 7 patients with dystonic flexion of the little and r ing fingers showed loss of silent periods between poorly formed bursts in FDS or EDC. Surprisingly, 9 of 10 patients with ulnar neuropathy s howed burst pattern abnormalities qualitatively similar to those obser ved in the dystonic patients. These data suggest that ulnar neuropathy alters the execution of a motor task involving multiple peripheral ne rves. (C) 1995 John Wiley & Sons, Inc.