A patient on parenteral nutrition containing glucose develops mental status changes after 3 days. The most likely vitamin deficiency is:

• A. Vitamin B6 (pyridoxine)
• B. Thiamine
• C. Folic acid
• D. Vitamin C

Answer: (B)

Thiamine is essential for metabolizing glucose. When patients receive parenteral nutrition with glucose, their brain’s demand for thiamine rises. If thiamine is deficient, that glucose can’t be efficiently processed through the pyruvate dehydrogenase and other enzymes, leading to brain energy failure and a rapid onset of mental status changes, which is classic for Wernicke’s encephalopathy in this setting. In parenteral nutrition, thiamine should be provided before or with glucose to prevent this.

Other vitamin deficiencies don’t typically cause this acute neurologic change in the short term: B6 deficiency tends to cause neuropathy or seizures but not the abrupt encephalopathy seen after glucose loading; folic acid deficiency mainly causes macrocytic anemia; vitamin C deficiency leads to scurvy symptoms rather than acute mental status changes.