Hemiballismus is a violent, involuntary movement restricted to one side of the body. Usually, it is most marked in the upper limb and in proximal joints.
The sudden, continuous projections of the limb may exhaust the patient and cause trauma to skin and joints. Movements may continue during sleep.
The classical cause of hemiballismus is damage to the contralateral subthalamic nucleus. Strokes are a common cause in elderly patients.
Treatment includes intravenous diazepam and oral haloperidol.