CORTICAL EXCITABILITY IN PATIENTS WITH ESSENTIAL TREMOR

We used transcranial magnetic stimulation in 10 patients with essentia l tremor and 8 matched healthy subjects. A round stimulating coil was placed over the vertex and electromyographic activity was recorded fro m the first dorsal interosseous muscle. Paired transcranial stimuli we re delivered at interstimulus intervals of 3, 5, 20, 100, 150, and 200 ms. The intensity of the conditioning stimulus was 80% of motor thres hold at short and 150% at long interstimulus intervals (ISIs). We also measured the silent period obtained after a single magnetic pulse del ivered at 150% of motor threshold during a submaximal muscle contracti on. Patients and controls had similar motor threshold and similar late ncies. Paired magnetic stimuli given at short and long ISIs at rest, a nd during a voluntary muscle contraction, elicited similar responses i n both groups. The silent period evoked by transcranial magnetic stimu lation had a similar duration in patients with ET and controls. In con clusion, these findings suggest that patients with essential tremor ha ve normal cortical motor area excitability. (C) 1998 John Wiley & Sons , Inc.