Visuomotor performance in patients with essential tremor

Essential tremor (ET) is the most prevalent extrapyramidal disorder, yet its diagnosis is still controversial. This article introduces new findings that pertain to this diagnostic problem. Twenty-three patients with ET were studied. Patients with parkinsonism, cerebellar signs, severe head injury, or those under neuroleptic medication were excluded. Twenty-five normal subjects served as control subjects. Visuomotor tests involving tracking and tracing along three different paths with both the right and left hands, were used. Performance was assessed by measuring test duration, directional error, the proportion of the cumulative test time during which directional error exceeded half the maximal possible level (PT50%), the mean distance from the model path, the velocity of the hand movement, and the number of tracking interruptions. In 15 of 23 patients performance was the same as in the control subjects. These patients were defined as having a "simple condition" of ET (ETs). Considerable visuomotor impairment was found in eight patients who were regarded as having a "complex condition" of ET (ETc). Patients with ETc had significantly lower tracking speed, more tracking interruptions, longer test duration, greater directional error, greater PT50%, and greater distance from path than patients with ETs or control subjects. Most patients with ET appear to have normal visuomotor capabilities (ETs) but some display significant visuomotor disturbances (ETc). Considering the presence of similar impairments in patients with early Parkinson's disease and the increased prevalence of parkinsonism in patients with ET, it is possible that preclinical parkinsonism exists in patients with ETc. Further follow up of patients with ETc is necessary to verify this possibility.