A 30-year-old chronic alcoholic is brought to the emergency department with confusion, ophthalmoplegia, and ataxia. Intravenous dextrose is started, and his condition acutely worsens. Deficiency of which vitamin is responsible, and why does glucose administration precipitate deterioration?

• A Vitamin B12; glucose impairs methylcobalamin-dependent myelin synthesis
• B Niacin (B3); glucose increases NAD+ consumption in glycolysis, worsening pellagra
• C Riboflavin (B2); glucose oxidation requires FAD, which is already deficient
• D Vitamin B1 (thiamine); glucose administration increases demand for thiamine-dependent enzymes, depleting already marginal stores ✓

Explanation

The triad of confusion, ophthalmoplegia, and ataxia is Wernicke's encephalopathy from thiamine (B1) deficiency. Thiamine pyrophosphate (TPP) is an essential cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase. Administering glucose without thiamine increases pyruvate flux through pyruvate dehydrogenase, rapidly exhausting the marginal thiamine reserve and precipitating Korsakoff psychosis or death. IV thiamine must always precede glucose in suspected Wernicke's.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.