Hemiballismus is unilateral ballismus, an involuntary hyperkinetic movement disorder in which there are large amplitude, vigorous ("flinging") irregular movements. Hemiballismus overlaps clinically with hemichorea ("violent chorea"); the term hemiballismus- hemichorea is sometimes used to reflect this overlap. Hemiballismic limbs may show a loss of normal muscular tone (hypotonia).
Anatomically, hemiballismus is most often associated with lesions of the contralateral subthalamic nucleus of Luys or its efferent pathways, although there are occasional reports of its occurrence with lesions of the caudate nucleus, putamen, globus pallidus, lentiform nucleus, thalamus, and precentral gyrus; and even with ipsilateral lesions. Pathologically, vascular events (ischemia, hemorrhage) are the most common association but hemiballismus has also been reported with space-occupying lesions (tumor, arteriovenous malformation), inflammation (encephalitis, systemic lupus erythematosus, post-streptococcal infection), demyelination, metabolic causes (hyperosmolal nonketotic hyperglycemia), infection (toxoplasmosis in AIDS), drugs (oral contraceptives, phenytoin, levodopa, neuroleptics) and head trauma.
Pathophysiologically, hemiballismus is thought to result from reduced conduction through the direct pathway within the basal ganglia-thalamo-cortical motor circuit (as are other hyperkinetic involuntary movements, such as choreoathetosis). Removal of excitation from the globus pallidus following damage to the efferent subthalamic-pallidal pathways disinhibits the ventral anterior and ventral lateral thalamic nuclei which receive pallidal projections and which in turn project to the motor cortex.
Hemiballismus of vascular origin usually improves spontaneously, but drug treatment with neuroleptics (haloperidol, pimozide, sulpiride) may be helpful. Other drugs which are sometimes helpful include tetrabenazine, reserpine, clonazepam, clozapine, and sodium valproate.
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