A 62-year-old woman develops abrupt onset of violent, wild flinging movements of the left arm and leg. MRI demonstrates a small haemorrhage in the right subthalamic nucleus. Damage to which pathway best explains the contralateral hyperkinetic movement disorder?
- A Loss of excitatory drive from the subthalamic nucleus to the internal segment of the globus pallidus ✓
- B Loss of inhibitory output from the internal segment of the globus pallidus to the thalamus
- C Loss of dopaminergic input from the substantia nigra pars compacta to the putamen
- D Loss of Purkinje cell inhibition of the dentate nucleus
Correct answer: A. Loss of excitatory drive from the subthalamic nucleus to the internal segment of the globus pallidus
Explanation
The subthalamic nucleus provides excitatory glutamatergic input to the internal globus pallidus, part of the indirect basal ganglia pathway. When it is destroyed, GPi activity falls, thalamic inhibition is released, and excessive movement appears as contralateral hemiballismus. Option B describes reduced GPi output correctly as the downstream effect but not the site of the lesion, and options C and D correspond to parkinsonism and cerebellar disease respectively.
Reference: Ganong's Review of Medical Physiology, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.