The abnormal swinging, flinging, and jerking movements that are sometimes seen in Huntington chorea (a progressive disorder involving degeneration of nerve cells in the cerebrum) or other diseases affecting the basal ganglia (clusters of nerve cells deep within the brain). Ballistic movements are involuntary and uncontrollable. They are caused by irregular muscle contractions and most commonly affect the arms and legs as a result of inappropriate signals from the brain. The most common cause of hemiballismus (ballistic movement affecting one half of the body) is a stroke in a deep area of the brain called the subthalamic nucleus.
Hemiballismus is a condition characterized by the abrupt and involuntary jerking and twitching of the limbs, resulting from brain damage in the region below the thalamus, which serves as a relay for sensory information. Typically, hemiballismus affects only one side of the body, hence the name.