A patient receiving long-term total parenteral nutrition (TPN) without supplementation develops confusion, ophthalmoplegia, and ataxia. Which vitamin deficiency is most likely, and what is the specific biochemical test to confirm subclinical deficiency before overt symptoms appear?
- A Vitamin B12; serum methylmalonic acid and homocysteine elevated
- B Thiamine (B1); erythrocyte transketolase activity with TPP activation effect ✓
- C Riboflavin (B2); erythrocyte glutathione reductase activity coefficient
- D Folate; erythrocyte folate level below 100 nmol/L
Explanation
The triad of confusion, ophthalmoplegia, and ataxia (Wernicke's encephalopathy) is the classical presentation of acute thiamine (vitamin B1) deficiency. TPN without thiamine supplementation causes rapid depletion because thiamine body stores are minimal (~18-20 mg total). Confirmation of subclinical thiamine deficiency uses the erythrocyte transketolase assay: low baseline activity confirms depletion, and the TPP activation effect (TPPE > 25% increase after adding TPP in vitro) indicates functional deficiency. This test is more sensitive than serum thiamine. Treatment is immediate IV thiamine before glucose administration (glucose may precipitate acute Wernicke's in deficient patients).
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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Written and medically reviewed by the StethoPrep medical team.