A 68-year-old hypertensive man suddenly develops violent, flinging movements of the left arm and leg. MRI shows a small haemorrhage on the right side. Which structure is most likely involved?

• A Substantia nigra pars compacta
• B Globus pallidus externa
• C Ventrolateral nucleus of thalamus
• D Subthalamic nucleus ✓

Explanation

Hemiballismus results from a contralateral lesion of the subthalamic nucleus, classically a small hypertensive haemorrhage from its supplying artery. The subthalamic nucleus normally exerts excitatory drive on the globus pallidus interna; its loss disinhibits the thalamus and produces wild proximal choreiform movements. Substantia nigra degeneration causes parkinsonism, not ballismus, and a thalamic lesion causes sensory loss or tremor rather than flinging movements.

Reference: Ganong's Review of Medical Physiology, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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