Abstract
Orthostatic tremor (OT) is a clinically defined syndrome of leg tremor while standing. Controversy surrounds whether OT is a distinct syndrome or is an essential tremor (ET) variant. We report two patients with OT. Electrophysiological testing included polymyography, accelerometry, nerve conduction, and evoked potential studies. The effects of various maneuvers and body positions on the tremor were assessed. The findings included rapid (15โ17 Hz) lowerโextremity tremor burst frequency evoked by standing but not by walking or swaying; rapid upperโextremity burst pattern synchronous with lowerโextremity bursts; and failure of electrical stimulation or mental concentration to โresetโ the tremor. Additionally, there was the novel finding of accelerometric recordings in the legs revealing the same rapid frequency (16โ17 Hz) as the electromyographic tremor bursts. Some prior reports have suggested that OT is related to ET by emphasizing a considerable disparity and variability between the accelerometric tremor frequency and the electromyographic burst frequency. In our patients, however, the rapid (15โ17 Hz) accelerometerโrecorded tremor synchronous with the electromyographic bursts, and also the clinical improvement with clonazepam but not beta blockers or mysoline, and the lack of a family history of ET provide support that OT is distinct from ET.