A 74-year-old man is admitted to emergency because of hematochezia for the past 24 hours. He has COPD and ischemic heart disease. Current medications are lisinopril, metoprolol, aspirin, and simvastatin. He is afebrile. Pulse is 90. Blood pressure is 135/90. Abdominal examination shows no abnormalities. Rectal examination shows clots and dark blood. The bleeding resolves spontaneously 4 hours after admission. Which of the following is the most likely diagnosis?
CMV colitis
Diverticulitis
Ischemic colitis
Pseudomembranous colitis
Ulcerative colitis
