Symposium on diarrhea. 3. Investigation of chronic diarrhea.

The practical approach to the investigation of diarrhea must be logical and based on anatomic considerations. The site of the underlying disorder may be determined by the clinical picture, and the logic of investigation will be influenced by the history. Important specific investigation in a case of colonic diarrhea include a careful rectal examination, stool inspection, sigmoidoscopy, rectal biopsy and barium enema study. Colonoscopy has been used, but its role has yet to be defined. In a case of small-bowel steatorrhea or diarrhea quantitative chemical estimation of the daily output of stool fat is useful, and to this investigation is added a small-bowel radiograph series and, if the radiographic findings are abnormal, small-bowel biopsy. Other investigations for small-bowel disease may include the breath test with carbon-14-labelled glycocholic acid, the lactose tolerance test, duodenal aspiration for giardiasis, analysis of serum immunoglobulins and, on occasion, isolation of vasoactive intestinal polypeptide hormone (which may aid the diagnosis of functioning tumours of the pancreas or small bowel). Investigations for pancreatic steatorrhea include abdominal radiography, performance of the secretin test and testing of the response to pancreatic replacement therapy. In some patients it may be useful to use endoscopic retrograde cholangiopancreatography to differentiate pancreatic carcinoma and chronic pancreatitis.