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Note the profound vertical and horizontal nystagmus in this video. It was due to Wernicke encephalopathy, a condition caused by vitamin B1 (thiamine) deficiency. Symptoms and findings include: confusion, ataxia, ophthalmoplegia, nutritional depletion. 2 of 4 need to be present in order to make the diagnosis. It usually develops over days to weeks. Exam may be remarkable for: confusion (range from mild to severe), cranial nerve palsy (CN 3, 4, 6--> impaired extra occular movements), nystagmus, ataxia, peripheral neuropathy.

Image Credit
Charlie Goldberg, M.D.