Review Question - QID 215061

A 65-year-old man presents to the clinic for 2 months of numbness in his feet. He has also had a depressed mood for the past 6 months. His current medical conditions include cirrhosis with a history of multiple prior hospitalizations for acute hepatitis. He takes no medications. He drinks a 6 pack of beers every night, which he has done for 45 years. He frequently skips meals to drink alcohol. The patient’s temperature is 96.0°F (35.6°C), blood pressure is 110/68 mmHg, pulse is 72/min, and respirations are 16/min. There is diminished sensation to light touch bilaterally over his toes and feet. The ankle jerk reflex is absent bilaterally. Laboratory studies reveal a deficiency of the coenzyme necessary for the reaction shown in Figure A. Which vitamin B provides the necessary coenzyme for this reaction?