Kaplan USMLE Step 3: Man with alcoholism confused and unable to walk

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

A 53-year-old man with a history of chronic alcoholism is brought to the emergency department after being found on the street, confused and unable to walk. He is unable to give a coherent history. On examination, he is confused, easily distracted and tangential. His temperature is 37.4ºC (99.3ºF), blood pressure is 150/90 mm Hg, pulse is 68/min and oxygen saturation is 95% on room air. Cardiac, pulmonary and abdominal exams are normal. Evaluation of ocular movements reveals bilateral lateral gaze palsy and horizontal nystagmus. His gait is shuffling and broad-based, but he shows no dysmetria. His neurologic exam is otherwise nonfocal. CT scan of the head without contrast shows no acute bleeding or evidence of stroke. A complete electrolyte panel reveals:

• Sodium: 134 mEq/L
• Potassium: 4.9 mEq/L
• Chloride: 102 mEq/L
• Bicarbonate: 28 mEq/L
• BUN: 48 mg/dL
• Creatinine: 1.6 mg/dL
• AST: 105 U/L
• ALT: 30 U/L

Which of the following is the most appropriate diagnostic method to ascertain this patient's diagnosis?

A. Electroencephalogram

B. Erythrocyte transketolase activity

C. MRI of the brain

D. No additional diagnostic tests are necessary

E. Serum thiamine

The correct answer is D.

This patient is presenting with new onset of confusion, ataxia and oculomotor dysfunction, a triad that is highly suggestive of Wernicke encephalopathy (WE). The diagnosis may be confounded by alcohol intoxication or acute withdrawal. The diagnosis of WE is made on clinical grounds only (no additional diagnostic tests are necessary), and only 30% of all patients have all three components of the classic triad. Clinical suspicion, therefore, should be high in patients with alcoholism and nutritional deficiency. The encephalopathy may range from inattentiveness and agitation to more rare cases of stupor and coma. Oculomotor findings typically consist of nystagmus and conjugate gaze palsies. Ataxia usually is limited to gait disturbance, so classic cerebellar dysmetria may be absent. Treatment usually includes Thiamine 200mg IV over 24 hours.

Choice A. Although helpful in determining the presence and type of seizure activity, electroencephalogram has limited value in other clinical settings. In the present patient you would expect to see either a normal study or nonspecific general slowing consistent with intoxication or chronic atrophy. No specific EEG changes associated with WE have been identified.