Alterations of ballistic movements in epileptic patients with phenytoin intoxication

We assessed the effects of phenytoin (PHT) overdosage on ballistic arm abduction movements in nine epileptic patients receiving long-term PHT treatment. During the overdosage period, all but one showed clinical abnormalities referable to impaired cerebellar function; one also had slowness of movement. Ballistic movements showed abnormalities in all of the patients although a great variability was present in the type and severity of abnormalities. In four patients, kinematic and EMG recordings differed least from the normal, in four they resembled those described in patients with cerebellar deficits, and in one those described in patients with Parkinson disease. The type and severity of clinical disturbances of voluntary motor control as well as alterations of ballistic movements were not related to specific PHT plasma concentrations. One month after the adjustment of PHT dosage, the patients who had clinical abnormalities completely recovered or markedly improved. Previously observed kinematic and EMG abnormalities completely disappeared or improved markedly.