GASTROENTEROLOGY 1

A 45-year-old white male comes to your office for evaluation of diarrhea of 8-months duration. He says that he has lost almost 15 lbs during the past 8 months. He denies any blood in the stools. 24-hour stool collection reveals fecal fat of 10 gm/day. Stool microscopy reveals no pathogens and no leucocytes. D-xylose test was performed which shows that less than 2 grams of D-xylose is excreted in urine in 5 hours. D-xylose test was re-performed after treatment with antibiotics but excretion is still less than 2 grams in 5 hours. Based on these findings, what is the most likely diagnosis in this patient?

A.  Lactose intolerance
B.  Bacterial overgrowth
C.  Pancreatic insufficiency
D.  Whipple’s disease
E.  Terminal ileal disease


The answer is D.
Whipple’s disease

Explanation:

Lactose intolerance may result in chronic diarrhea, but fecal fat will not be high in such causes (Option A).

Bacterial overgrowth, pancreatic insufficiency, Whipple’s and Crohn’s disease all result in chronic diarrhea with increased fecal fat content. D-xylose is a simple sugar. It does not need to undergo any digestive process before it can be absorbed. Its absorption requires an intact mucosa only.

In normal individuals, after ingestion of 25 grams of D-xylose, its urinary excretion will be greater than 4.5 grams in 5 hours. In pancreatic insufficiency, there is deficiency of pancreatic enzymes, which lead to impaired digestion of fats. D-xylose absorption remains unimpaired, as there is no damage to small intestinal mucosa.

In terminal ileal disease, bile salts are decreased due to impaired enterohepatic circulation, and as a result absorption of fats will be impaired. In bacterial overgrowth there will be both impaired fat absorption due to bacterial de-conjugation of bile salts as well as decreased excretion of xylose due to bacterial consumption of the simple sugar. In such cases, urinary excretion of xylose returns to normal after treatment with antibiotics. In the above case, urinary exertion of D-xylose does not increase after treatment with antibiotics and bacterial overgrowth is therefore ruled out. Whipple’s disease damages small intestinal mucosa, thus impairing D-xylose absorption (Option D).