Chronic Diarrhea

An 82-year-old active man is referred for evaluation of a 6-month history of loose, watery stools without blood; before this he had no gastrointestinal symptoms. He has had a 10-pound weight loss during this period of time. He denies any abdominal pain, nausea, or vomiting. Colonoscopy 15 years previously was “normal.” He has started no new medications during the immediate months preceding the onset of his diarrhea. His medical history is notable for coronary artery disease, hypertension, and hyperlipidemia. He takes simvastatin, lisinopril, metoprolol, clopidogrel, and aspirin. He drinks a cocktail every evening and denies tobacco use. Physical examination is unremarkable. His hematocrit is 37%, and white cell count is 6.7 × 10⁹/L. The chemistry panel including liver function tests and thyroid-stimulating hormone is normal. Stool cultures are negative for ova and parasite, Clostridium difficile, enteric pathogens, and white blood cells. Fecal fat excretion in a 24-hour stool collection is 28 g.