Water-soluble vitamin deficiency and toxicity Quiz: Ace Your Exams

A 36-year-old man is brought in by his roommate to the emergency department with acute-onset mental status changes. The roommate states the patient rarely eats whole meals and typically only eats canned soups. He has been drinking 7-8 beers daily for the past 20 years. He occasionally uses cocaine and injectable heroin. Temperature is 37.0°C (98.6°F), pulse is 80/min, respirations are 20/min, and blood pressure is 125/85 mmHg. He is confused and disoriented to time, place and person. Pupils are equal and reactive, and horizontal nystagmus is elicited on lateral gaze. Lateral gaze is restricted on both sides. Fundoscopy is normal. Motor strength is 3/5 in the lower limbs and 5/5 in the upper limbs bilaterally. Deep tendon reflexes are absent at the ankles bilaterally. Romberg sign is negative. Finger-to-nose and heel-to-shin testing are normal. The patient’s gait is wide-based. There is no nuchal rigidity on examination. Rapid glucose test is 60 mg/dL. Which of the following is the most likely etiology of this patient’s clinical presentation?