Review Question - QID 214895

A 38-year-old man presents to a new primary care physician with a 2-year history of intermittent diarrhea and abdominal pain. He also complains of pain in his bones and difficulty with his vision, especially at night. His past medical history is significant for amphetamine, alcohol, and opioid use. Social history reveals that he has been transiently homeless for several years and has not seen a doctor in that time. Physical exam reveals a thin individual with diffuse bruising and poor dentition. Laboratory findings reveal a serum lipase of 490 U/L (normal range: 0-160 U/L). Which of the following is the most likely underlying cause of this patient's symptoms?