A 71-year-old man on the geriatric behavioral inpatient unit displays ataxia, vestibular dysfunction, and a variety of ocular motility abnormalities such as horizontal nystagmus and a sluggish reaction to light. He has a 40-year history of alcohol abuse. What is his most likely diagnosis?

Choice A reason: Creutzfeldt-Jacob disease is a rare neurodegenerative disorder caused by prion proteins. It presents with rapidly progressive dementia, myoclonus, and motor dysfunction, but does not typically include the classic triad of Wernicke’s encephalopathy. Choice B reason: Lewy body dementia is characterized by fluctuating cognition, visual hallucinations, and parkinsonian features. While it may include motor and cognitive symptoms, it does not typically present with the acute ocular and vestibular signs seen in Wernicke’s encephalopathy. Choice C reason: Wernicke’s encephalopathy is a neurologic emergency caused by thiamine deficiency, often due to chronic alcohol abuse. The classic triad includes ophthalmoplegia (e.g., nystagmus), ataxia, and confusion. The patient’s history and symptoms strongly support this diagnosis. Choice D reason: Delirium is an acute disturbance in attention and cognition, often reversible and multifactorial. While it may coexist with Wernicke’s encephalopathy, it does not explain the specific ocular and vestibular findings.