Unilateral asterixis associated with a mesencephalic syndrome.

Unilateral asterixis due to a focal brain lesion is a rare occurrence. Acute asterixis restricted to the left upper extremity appeared in a patient in association with signs of acute midbrain dysfunction, without changes in mental status or in the EEG, and in the absence of metabolic or toxic disturbance. Electromyography disclosed features typical of asterixis due to metabolic causes.