MYOCLONIC-LIKE FINGER MICRODISPLACEMENTS IN PATIENTS WITH CEREBELLAR DEFICITS

Background: Here we assess the ability of patients with cerebellar dis ease to execute a simple visually-guided movement task involving track ing of a target with the index finger. Methods: Spontaneous microdispl acements in index finger position are compared in patients with cerebe llar deficits (ischemia [n = 3], multiple sclerosis [n = 3], degenerat ive cerebellar disease [n = 3]) and age matched healthy subjects. Subj ects were required to maintain a constant finger position relative to a stationary baseline displayed on an oscilloscope. Results: Unusual t ransient abrupt movements (sac cadic or myoclonic-like) directed with or against gravity were seen in patients whose neurological deficits w ere the most severe (7/9 patients). These abrupt myoclonic-like moveme nts occurred independently of visual input, were not associated with c linically observable myoclonus, and were not detected previously in pa tients with Parkinson's disease. These abrupt myoclonic-like movements were not associated with abnormalities in either physiological tremor , or oscillations in finger microdisplacements induced by insertion of a delay (300-1400 ms) into the visual feedback of this finger ''holdi ng'' experiment. An unexpected finding is that the results obtained fo r patients with cerebellar deficits by insertion of an experimental de lay are not significantly different from those obtained with their age -matched controls. Conclusions: These observations suggest that abrupt myoclonic-like movements are a characteristic abnormality of patients with a variety of cerebellar deficits and emphasize the value of this simple motor tracking task for characterizing movement disorders.