It is considered one of the most severe forms of chorea, and is characterised by violent movements of the axial or proximal limb musculature, often described as "flinging" in nature.
Movements can be unilateral - "hemi-ballismus" or more rarely, bilateral - "biballism or paraballism"
Usually caused by a lesion in the contralateral subthalamic nucleus.
The subthalamic nucleus provides excitatory stimulation to the globus pallidus interna (GPi). The reduced discharge to the GPi reduces its inhibitory effect on the thalamus. This reduction in thalamic inhibition causes unrestricted motor movements.
CT scan and MRI - exclude vascular or other localised lesions
Lumbar puncture - exclude TB meningitis in patients with risk factors