The phenomenology of task-specific tremor—what’s in a name?

BackgroundTask-specific musicians’ tremor and primary writing tremor are unusual forms of tremor triggered by performance of a specific task. Whether these disorders fit within the dystonia rubric or are related to essential tremor remains a matter of debate.MethodsDemographic and clinical features of 56 newly reported patients included 23 musicians with task-specific tremor, 30 patients with primary writing tremor, and 3 patients with task-specific tool tremor. These features were compared with similar cohorts of essential tremor, writer’s cramp, focal task-specific musicians’ arm dystonia, isolated voice tremor and embouchure tremor.ResultsIsolated tremor syndromes share common clinical features, including a family history of tremor, response of tremor to ethanol, and similar tremor frequency. Review of task-specific tremor patient videos in slow motion revealed under-recognized clinical features consistent with a diagnosis of essential tremor (e.g. mild postural tremor, action tremor and voice tremor). In more than 90% of patients, task-specific tremor was triggered just by positioning the arm in the specific posture required to perform the task (i.e. tremor was position induced, not linked solely to performance of the task). Clinical and demographic features of patients with isolated tremor disorders differed significantly from writer’s cramp and musicians’ task-specific dystonia.ConclusionsTask-specific tremor disorders share common clinical and demographic features with one another and with essential tremor Task-specific tremors differ in demographic and clinical phenotype from writer’s cramp and musicians’ dystonia. We suggest the possibility that task-specific tremors may be “form frustes” of essential tremor rather than dystonia.