A 40-year-old chronic alcoholic presents with confusion, ophthalmoplegia, and ataxia. He is treated with IV thiamine. After partial improvement, he is noted to have anterograde amnesia and confabulation. Which specific structural lesion explains the persistent amnestic syndrome?

• A Cerebellar vermis atrophy
• B Bilateral mammillary body necrosis extending to mediodorsal thalamic nuclei ✓
• C Hippocampal sclerosis due to glutamate excitotoxicity
• D Corpus callosum demyelination (Marchiafava-Bignami disease)

Explanation

Wernicke's encephalopathy (ophthalmoplegia, ataxia, confusion) results from acute thiamine deficiency. The neuropathological hallmark is haemorrhagic necrosis of the periventricular grey matter, specifically the mammillary bodies and mediodorsal thalamic nuclei. Incomplete treatment leads to Korsakoff's syndrome: severe anterograde > retrograde amnesia and confabulation, due to permanent structural damage to the mammillary bodies and mediodorsal thalamus — structures critical for memory consolidation. Cerebellar vermis atrophy also occurs in alcoholics but causes gait ataxia, not the amnestic syndrome.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.