Acute hemiballismus in the absence of subthalamic nucleus lesion

A 68-year-old male, known hypertensive on irregular medication presented with sudden onset of involuntary movements of the left upper limb, in the form of severely violent, arrhythmic, and flinging large amplitude movements for 2 days, suggestive of hemiballismus. Magnetic resonance image of brain revealed a subacute nonhemorrhagic infarct in the posterior limb of the right internal capsule, but no lesion was noted in the subthalamic region. In traditional teaching, hemiballismus has been characterized as almost pathognomonic of a lesion in the subthalamic nucleus (STN). While a lesion occurring directly in the subthalamic nuclei can explain the onset of the movement disorder, a lesion occurring anywhere along the cortico-striatal pathway can also produce similar symptoms. The prognosis is benign in most cases, with almost all patients responding well to treatment and many having spontaneous remission. Our patient improved significantly following Tetrabenazine. Hemiballismus is as such a rare movement disorder. An elderly patient with sudden onset hemiballismus, indicating a vascular insult confirmed by subacute infarct in the posterior limb of the internal capsule, without any lesion in STN merits the report of this rare case.