A 25-year-old male presents with an 18-month history of chro…
A 25-year-old male presents with an 18-month history of chronic abdominal pain. The patient has seen several providers and has been diagnosed as having ‘nervous stomach’, irritable bowel syndrome, and depression. Associated with this abdominal pain for the last 3 months have been non-bloody diarrhea, anorexia, and a weight loss of 20 lbs. On exam, the patient has diffuse abdominal tenderness. He looks thin and unwell. He has a tender, erythematous area in the right perirectal area suggestive of a rectal abscess. Which of the following investigations is the most sensitive test for confirming the diagnosis in this patient?