POSTURAL TREMOR OF PARKINSONS-DISEASE

Previous studies have reported the resting tremor (RT) of Parkinson's disease to occur at frequencies between 3-7 Hz and to be characterised by an alternating pattern of electromyographic (EMG) bursting activit y between opposing muscles. A postural tremor (PT), of higher frequenc y (>6 Hz) and with a synchronous pattern of EMG activity, has also bee n previously described in Parkinson's disease. We investigated the ele ctrophysiological and pharmacological properties of both the RT and PT of 11 patients with Parkinson's disease and 10 patients with essentia l tremor in a double-blind, placebo-controlled study of L-Dopa/bensera zide and propranolol. Tremor amplitude and frequency were assessed via bidirectional accelerometry, and the pattern of activation of the ant agonist muscles of the forearm was determined with use of surface EMG. In the Parkinson's disease group studied, the frequency, EMG pattern of bursts, and response to L-Dopa were similar for the two tremors (me dian improvement of RT by 70% and PT by 61%). Despite some overlap bet ween the Parkinson's disease and essential tremor groups in the electr ophysiology of the tremor, there was no such dramatic pharmacological response in the latter group. These results suggest that the RT and PT of Parkinson's disease share a common pathophysiology and are distinc t from essential tremor.