Hemiballismus or hemiballism is a basal ganglia syndrome resulting from damage to the subthalamic nucleus in the basal ganglia. Hemiballismus is a rare hyperkinetic movement disorder, that is characterized by violent involuntary limb movements, on one side of the body, and can cause significant disability. Ballismus affects both sides of the body and is much rarer. Symptoms can decrease during sleep.Hemiballismus differs from chorea in that the movements occur in the proximal limbs whereas in chorea the limb movements are in the distal limbs. Also in chorea the movements are more dance-like, flowing from one region to another. Presentation
Ballism was defined by Meyers in 1968 as "Repetitive, but constantly varying, large amplitude involuntary movements of the proximal parts of the limbs. This activity is almost ceaseless and movements are often complex and combined". Hemiballismus is usually characterized by involuntary flinging motions of the extremities. The movements are often violent and have wide amplitudes of motion. They are continuous and random and can involve proximal or distal muscles on one side of the body. Some cases even include the facial muscles. It is common for arms and legs to move together. The more a patient is active, the more the movements increase. With relaxation comes a decrease in movements. Physicians can measure the severity of the disorder by having the patient perform a series of basic, predetermined tasks and counting the hemiballistic movements during a set time session. The physicians then rate the patient on a severity scale.
Research is being done in these areas in order to give scientists and clinicians a better model for this disease that will ultimately lead to better diagnosis and treatment of this disorder. Research is also being done on why certain treatments seem to help hemiballistic patients when they should seemingly do more harm. An example of this is why lesioning the globus pallidus seems to reduce hemiballistic movements. The mechanism behind the effect of dopamine on patients symptoms remains unknown. History
The work of J.R. Whittier, F.A. Mettler, and M.B. Carpenter in the mid-1900s helped scientists and clinicians form a more complete picture of hemiballismus. In their experiments, several lesions were made in the basal ganglia structures in monkeys and then they monitored the results. They noticed that the majority of the time, the monkeys did not have any unusual movements. However, when at least twenty percent of the subthalamic nucleus was damaged, abnormal movements were seen in the limbs opposite to the side of the brain that was damaged. This observation caused scientists to believe that hemiballismus outside the subthalamic nucleus did not occur. It was not until much later that this classical model began to expand to include other areas of the basal ganglia and even some cortical structures. They also noticed that unlike human patients, the unusual movements in the monkeys were mainly in the lower extremities.