Case Presentation: An 80-year-old male with a history of collagenous colitis, hypertension, type 2 diabetes, microcytic anemia, exocrine pancreatic insufficiency, severe malnutrition, and vitamin D deficiency presented with weakness, chronic diarrhea, and significant weight loss (~100 lbs in one year). He had 5-7 non-bloody stools daily, unresponsive to colestipol and loperamide, accompanied by abdominal bloating [...]