A 45-year-old man with a 20-year history of alcohol use disorder presents to the emergency department with acute confusion, horizontal nystagmus, and inability to abduct both eyes. On examination, he is ataxic and disoriented to time and place. The structure marked **B** in the diagram is deficient, and its active form (thiamine pyrophosphate) is essential for the function of several metabolic enzymes. Which of the following is the MOST critical immediate management step in this patient?

Explanation

## Why "Administer high-dose intravenous thiamine 500 mg three times daily BEFORE any glucose administration" is right The patient presents with the classic triad of Wernicke encephalopathy: confusion, ophthalmoplegia (horizontal nystagmus and CN VI palsy with inability to abduct eyes), and ataxia. This is a medical emergency caused by deficiency of the structure marked **B** (Vitamin B1/Thiamine). Thiamine pyrophosphate (TPP) is the essential cofactor for pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, branched-chain α-keto acid dehydrogenase, and transketolase. In malnourished or chronic alcoholic patients, administering glucose BEFORE thiamine can precipitate or worsen Wernicke encephalopathy by triggering a sudden surge in thiamine-dependent metabolic flux without adequate cofactor availability. The standard emergency protocol is to give high-dose IV thiamine 500 mg three times daily for 2–3 days BEFORE glucose administration. This is a critical teaching point in emergency medicine and biochemistry (Harper 32e Ch 44; Harrison 21e Ch 333). ## Why each distractor is wrong - **Administer intravenous glucose 50% immediately to correct hypoglycemia and restore consciousness**: While glucose may be needed, administering it BEFORE thiamine in a malnourished/alcoholic patient with suspected Wernicke encephalopathy can precipitate or worsen the condition. Thiamine must be given first. - **Perform urgent CT head to rule out subdural hematoma before initiating any treatment**: Although head imaging may be warranted later, the clinical presentation (triad of confusion, ophthalmoplegia, ataxia in a chronic alcoholic) is pathognomonic for Wernicke encephalopathy. Delaying thiamine administration to obtain imaging risks irreversible neurological damage and progression to Korsakoff syndrome. - **Start empirical antibiotics for bacterial meningitis while awaiting CSF culture results**: The clinical triad and risk factor (chronic alcoholism) point to Wernicke encephalopathy, not meningitis. Meningitis would typically present with fever, neck stiffness, and CSF pleocytosis, which are not described here. **High-Yield:** In any malnourished or alcoholic patient with altered mental status, give IV thiamine BEFORE glucose to prevent precipitation of Wernicke encephalopathy. [cite: Harper 32e Ch 44; Harrison 21e Ch 333]