A 40-year-old man with a 20-year history of alcohol abuse is brought to the hospital by his friends because he was difficult to rouse. He ate a large meal several hours ago. He is emaciated and lethargic. Examination shows severely restricted horizontal eye movements and ataxia of both upper extremities. The most likely cause of these findings is a deficiency of which of the following nutrients?
A. Folic acid
B. Vitamin A
C. Vitamin B1 (thiamine)
D. Vitamin B6 (pyridoxine)
E. Vitamin B12 (cobalamin)
Correct answer : C. Vitamin B1 (thiamine)
The clinical features are characteristic of Wernicke encephalopathy seen in chronic alcoholics due to thiamine deficiency.