Rest tremor in patients with essential tremor: prevalence, clinical correlates, and electrophysiologic characteristics.

BACKGROUND Isolated rest tremor, which is observed in some patients with essential tremor (ET), poses a diagnostic challenge. The phenomenon has been examined in few studies and is poorly understood. OBJECTIVES To determine the prevalence and study the clinical correlates of rest tremor in ET and to examine the electrophysiologic features in a subgroup of patients. METHODS Sixty-four patients with ET cared for at a tertiary referral center underwent neurologic examination. Five of 12 patients with rest tremor also underwent quantitative computerized tremor analysis using accelerometry and handwritten spiral analysis. RESULTS Twelve of 64 patients with ET had rest tremor (prevalence, 18.8%; 95% confidence interval, 9.2%-28.4%). Compared with the 52 patients with ET without rest tremor, these 12 had disease of longer duration and greater severity. Also, their ET was more widely disseminated, as evidenced by a larger proportion with head tremor. None had clinical signs of bradykinesia or rigidity. The 5 patients with rest tremor who underwent electrophysiologic study had electrophysiologic features consistent with parkinsonism (eg, slow spiral speed and increased decrement of spiral speed with radius). CONCLUSIONS In our sample, 1 in 5 patients with ET had rest tremor. The tremor was associated with disease that was more severe, more disseminated, and of longer duration. Some of these patients had electrophysiologic features consistent with parkinsonism. The basis for the rest tremor could be basal ganglia involvement, raising the possibility that the pathologic process responsible for ET may extend to these structures.