Hemiballismus

Hemiballismus is a very rare movement disorder, classified by a decrease in activity of the subthalamic nucleus of the basal ganglia, resulting in decreased suppression of undesired movements. It is 500 times more rare than Parkinson's disease. Its effects can sometimes be severe enough to prevent patients from being able to perform daily functions. It is usually associated with structural brain lesions but can occur with metabolic abnormalities. The symptoms can also decrease while the patient is asleep, unlike some movement disorders.