A 40-year-old homeless man comes to the emergency department due to a "pins-and-needles" sensation in his legs. He also has painful lesions on his lips and corners of his mouth. He has had no loss of consciousness, nausea, vomiting, or diplopia. The patient drinks alcohol heavily on a daily basis and has a history of intravenous heroin use. On physical examination, he appears unkempt and ill appearing. Temperature is 36.8 C (98.2 F), blood pressure is 146/90 mm Hg, and pulse is 106/min. He has glossitis and angular stomatitis. Abdominal examination reveals hepatomegaly. Laboratory evaluation shows very low urinary riboflavin excretion. Activity of which of the following enzymes is most likely directly impaired in this patient?

Question

A 40-year-old homeless man comes to the emergency department due to a "pins-and-needles" sensation in his legs.  He also has painful lesions on his lips and corners of his mouth.  He has had no loss of consciousness, nausea, vomiting, or diplopia.  The patient drinks alcohol heavily on a daily basis and has a history of intravenous heroin use.  On physical examination, he appears unkempt and ill appearing.  Temperature is 36.8 C (98.2 F), blood pressure is 146/90 mm Hg, and pulse is 106/min.  He has glossitis and angular stomatitis.  Abdominal examination reveals hepatomegaly.  Laboratory evaluation shows very low urinary riboflavin excretion.  Activity of which of the following enzymes is most likely directly impaired in this patient?

Quizplus · Accepted Answer

Eductional Objective: Riboflavin is a precursor of the coenzymes FMN and FAD.  FAD participates in the tricarboxylic acid cycle and electron transport chain by acting as an electron acceptor for succinate dehydrogenase (complex II), which converts succinate into fumarate.

A 40-Year-Old Homeless Man Comes to the Emergency Department Due