A 68-year-old hypertensive woman suddenly develops wild, flinging, involuntary movements of the left arm and leg. MRI shows a small haemorrhage in the right diencephalon. Which nucleus is most likely involved?

• A Subthalamic nucleus ✓
• B Ventral lateral nucleus of the thalamus
• C Globus pallidus internus
• D Red nucleus

Explanation

Contralateral hemiballismus classically follows a lesion of the contralateral subthalamic nucleus, usually a small hypertensive haemorrhage. The subthalamic nucleus exerts excitatory drive on the GPi, so its loss removes GPi inhibition of the thalamus and produces the large-amplitude proximal movements. B ventrolateral thalamic lesion produces tremor or sensory loss, and a red nucleus lesion produces tremor and ataxia, not ballism.

Reference: Snell's Clinical Neuroanatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.