How is chronic fatty diarrhea evaluated
Chronic fatty diarrhea is due to either maldigestion or malabsorption.
Maldigestion can occur with pancreatic exocrine insufficiency, with ingestion of the lipase inhibitor orlistat, or if there is a bile acid deficiency, which reduces fat emulsification.
Malabsorption typically is due to mucosal diseases such as celiac disease, small intestinal bacterial overgrowth, or small bowel fistula or resection.
Pancreatic exocrine insufficiency can be evaluated with a secretin test or measurement of chymotrypsin or elastase in stool. Because these tests are not widely available or have poor specificity and sensitivity, clinicians often resort to a therapeutic trial of pancreatic enzymes.
If this is done, the patient should be treated with a high dose of enzymes and the effect of this treatment on stool fat excretion as well as symptoms should be assessed.
Bile acid deficiency is a rare cause of maldigestion and is best assessed by direct measurement of duodenal bile acid concentration postprandially. Tests showing excess bile acid excretion in stool (radiolabeled bile acid excretion or total bile acid excretion tests) do not directly assess duodenal bile acid concentration, but if fecal bile acid excretion is high, reduced duodenal bile acid concentration can be inferred. Mucosal disease can be evaluated with small bowel biopsy and bacterial overgrowth can be assessed by breath hydrogen testing after an oral glucose load or by quantitative culture of intestinal contents