Thiamine deficiency
USMLE Step 1Difficulty: mediumLast updated:
A 49-year-old man with long-standing alcohol use disorder is brought to the emergency department because of confusion and unsteady gait. Examination shows horizontal nystagmus, bilateral lateral rectus palsies, and a wide-based ataxic gait. He is apathetic and disoriented to time.
Which of the following laboratory findings would best confirm the vitamin deficiency responsible for his condition?
Answer and explanation
Correct answer: C. Decreased erythrocyte transketolase activity
Confusion, ophthalmoplegia, nystagmus, and ataxia in a person with alcohol use disorder are the classic features of Wernicke encephalopathy, caused by thiamine (vitamin B1) deficiency. Thiamine pyrophosphate is a cofactor for enzymes of carbohydrate metabolism, including transketolase in the pentose phosphate pathway. The source states that erythrocyte transketolase activity (low in thiamine deficiency) and 24-hour urinary thiamine excretion can be measured to confirm equivocal cases. Treatment should not wait for the result. Because thiamine is necessary for glucose metabolism, glucose infusions may precipitate or worsen symptoms, so at-risk patients should receive IV thiamine 100 mg before IV glucose.
Each option explained
- A. Decreased erythrocyte glutathione reductase activityIncorrect. Decreased erythrocyte glutathione reductase activity is used to assess riboflavin (B2) status.
- B. Decreased serum ceruloplasminIncorrect. Low ceruloplasmin supports Wilson disease, which does not cause acute ophthalmoplegia.
- C. Decreased erythrocyte transketolase activityCorrect. Low erythrocyte transketolase activity confirms thiamine deficiency.
- D. Elevated serum methylmalonic acidIncorrect. Elevated methylmalonic acid indicates vitamin B12 deficiency.
- E. Elevated homocysteine with normal methylmalonic acidIncorrect. Elevated homocysteine with normal methylmalonic acid suggests folate deficiency.
Key point
Wernicke encephalopathy is thiamine deficiency (low erythrocyte transketolase); give IV thiamine before glucose.
From the source
“erythrocyte transketolase activity (low with thiamine deficiency) and 24-hour urinary thiamine excretion may be measured”