Hemiballismus

Hemiballismus is a movement disorder characterised by unilateral wild, large amplitude flinging movements of the arm and leg, normally causing falls and preventing postural maintenance.

It is caused by a lesion or infarction in the subthalamic nucleus or its connections, usually in patients with a history of hypertension or diabetes, or following TB meningitis. The subthalamic nucleus normally regulates the globus pallidus by exciting the GPi, which in turn normally inhibits the ventral lateral nucleus of the thalamus. The reduced discharge in both causes disinhibition of the thalamus and consequent involuntary stimulation of the motor cortex. Altered dopaminergic feedback mechanisms may also be involved. [1]

Chemical treatment is via dopamine blockade, or via surgical lesions to the globus pallidus, lenticular fasciculus or VL nucleus of thalamus.