A 60 year old man presents with a gradual onset of difficulty walking which has worsened over the last few weeks to months. He feels weak, unsteady, and uncoordinated in his legs. He's also recently developed poor coordination of the arms, dysarthria, and intermittent diplopia and blurred vision. His past medical history is only significant for a few episodes of alcoholic hepatitis and a remote appendectomy. His social history is significant for being a heavy drinker for 25+ years.
On exam, he appears malnourished. Mental status and cognitive function are normal. On his cranial nerve exam, visual fields and acuity are intact, fundoscopic exam is normal, pupils are round and reactive to light, extraocular movements are intact, facial sensation is intact, muscles of mastication and muscles of facial expression are symmetric and strong, hearing is grossly intact, palate is midline and moves fully, head rotation and shoulder shrug are strong, and tongue movement is symmetric. He has slow, slurred speech and a coarse rhythmic 3-5 Hz postural tremor of the fingers. He has ataxia of stance and gait. He cannot do tandem walking. Heel-knee-shin testing is grossly abnormal, and finger-nose testing is mildly abnormal. His blood alcohol level is 0.
Administration of thiamine does not reverse this disease.
Challenge: Localize the lesion! What's your diagnosis?
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