ATYPICAL TREMOR

The tremor present in a small number of patients who present with feat ures of both Parkinson's disease (PD) and essential tremor (ET) is ill -defined. We therefore studied 8 such patients with 'atypical' tremor and compared them clinically to 11 PD and 10 ET patients in a double-b lind, cross-over, placebo-controlled trial. Tremor was assessed via ac celerometry and surface EMG. Tremor frequency and the acute tremorlyti c response to propranolol were not useful in discriminating between gr oups. Over 80% of atypical and PD patients showed alternating EMG, whe reas 90% of ET patients had synchronous EMG activity. Tremor amplitude improved by > 90% in 38% of atypical, 27% of PD and none of the ET pa tients after single-dose L-dopa/benserazide (300/75 mg), a response wh ich was significantly different between the ET and PD groups. Failure to differentiate electrophysiologically and pharmacologically between the atypical and other groups probably relates to clinical heterogenei ty in the atypical group.