MODULATION OF POSTURAL TREMORS AT THE WRIST BY SUPRAMAXIMAL ELECTRICAL MEDIAN NERVE SHOCKS IN ESSENTIAL TREMOR, PARKINSONS-DISEASE AND NORMAL SUBJECTS MIMICKING TREMOR

The response of postural wrist tremors to supramaximal median nerve st imulation was examined in patients with hereditary essential tremor (n = 10) and Parkinson's disease (n = 9), and in normal subjects mimicki ng wrist tremor (n = 8). The average frequency of on-going tremor was the same in all three groups. Supramaximal peripheral nerve shocks inh ibited and then synchronised the rhythmic electromyographic (EMG) acti vity of all types of tremor. The duration of inhibition ranged from 90 to 210ms, varying inversely with the frequency of on-going tremor. Th ere was no significant difference in mean duration of inhibition or in the timing of the first peak after stimulation on the average rectifi ed EMG records between the three groups. The degree to which supramaxi mal peripheral nerve shocks could modulate the timing of rhythmic EMG bursts in the forearm flexor muscles was also quantified by deriving a resetting index. No significant difference in mean resetting index of the three groups was found. These results suggest that such studies c annot be used to differentiate between the common causes of postural w rist tremors.