Task-specific tremor.

Task-specific tremor is a form of action tremor that occurs only or mainly when a person is performing a specific skilled task. The most frequently encountered form of task-specific tremor is primary writing tremor (PWT). Currently, there is debate about whether PWT is a variant of essential tremor, writer's cramp (dystonia), a separate entity, or in some cases related to essential tremor and in others to dystonia. PWT typically occurs at a frequency of 5-7Hz and has been subdivided into to two types: Type A, task-induced tremor, and type B, positionally sensitive tremor. Temporary suppression of the tremor by alcohol is seen in about one-third of cases. There are no randomized controlled therapeutic studies involving patients with PWT, although anecdotal reports of beneficial responses to propranolol, primidone, anticholinergics, botulinum toxin treatment, and stereotactic surgery have been reported. Reciprocal inhibition of the H-reflex and intracortical excitability are normal in PWT, unlike writer's cramp. Hyperactivity in the cerebellar hemispheres has been demonstrated with positron emission tomography in PWT. Other task-specific tremors have been described but have not been studied in detail.