Focal task-specific tremor and dystonia: categorization of occupational movement disorders.

We studied 28 patients with focal task-specific disorders. Three groups were identified, according to the occurrence of focal tremor alone (group I, n = 10), dystonia alone (group II, n = 8), and tremor-dystonia combination (group III, n = 10). Four of six patients in groups I and III showed improvement with beta blocking agents alone, and another patient improved with primidone and metoprolol. Four of seven patients in groups II and III improved at least moderately with only anticholinergic medication. The coexistence of focal tremor and focal dystonia in the same limb in 10 patients (group III) suggests a link between these focal disorders. We conclude that focal tremor and focal dystonia are related to generalized essential tremor and generalized dystonia. A scheme which conceptualizes these interrelationships is proposed.