RECIPROCAL INHIBITION IN WRITERS CRAMP

We studied the inhibition of median H-reflexes by conditioning stimuli on the radial nerve in 13 patients with writer's cramp, eight of the simple type and five of the dystonic type, acid in 14 normal volunteer s. The patients and controls were right-handed, and their right arms w ere studied. Asymptomatic left arms were also studied in nine of 13 pa tients. In the control group we identified three periods of inhibition , with maximum peaks at conditioning-test intervals of 0 ms (41 +/- 17 %), 20 ms (40 +/- 13%), and 100 ms (36 +/- 20%). In the patient group, the amplitudes of inhibition of these three periods in both arms were significantly less than those in the control group. However, there we re no significant differences in the amplitudes of inhibition of these three periods between symptomatic and asymptomatic arms. There were a lso no significant differences between simple and dystonic writer's cr amps. Our results indicate that the attenuation of reciprocal inhibiti on was present not only in symptomatic arms but also in asymptomatic a rms of patients with writer's cramp. The defect of reciprocal inhibiti on in the asymptomatic hand has never been documented. We suggest that the preexistent electrophysiological abnormality may provide an expla nation for the development of hand cramp after shifted writing.