A 45-year-old man comes to the clinic for evaluation of chronic diarrhea. He has lost almost 7 kg (15 lb) over the past year. He has no blood in the stool. A 24-hour stool collection shows fecal fat content of 10 g/day (normal

Question

A 45-year-old man comes to the clinic for evaluation of chronic diarrhea.  He has lost almost 7 kg (15 lb) over the past year.  He has no blood in the stool.  A 24-hour stool collection shows fecal fat content of 10 g/day (normal <6 g/day).  Stool microscopy shows no pathogens and no leukocytes.  Serum electrolytes and renal function are within normal limits.  The patient is given 25 g oral D-xylose solution, and his urinary excretion of D-xylose at 5 hours is 1.2 g (normal 4.5-7.5 g).  After 4 weeks of treatment with rifaximin, the D-xylose test is repeated, and the urinary excretion at 5 hours is 1.3 g.  Based on these findings, which of the following is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d3dc_0042_bc81_57e7b2d325f3_MD0003_00 This patient has chronic diarrhea, steatorrhea, and weight loss suggesting malabsorption. Celiac disease is a common cause of malabsorption and is characterized by atrophy of intestinal villi in the proximal small bowel due to exposure to gluten-containing wheat products. It is most common in patients of Northern European descent, and prevalence increases with age. D-xylose is a monosaccharide that can be absorbed in the proximal small intestine without degradation by pancreatic or brush border enzymes. It is subsequently excreted in the urine. In the D-xylose test, the patient is given an oral dose of D-xylose, with subsequent assay of urine and venous blood. Patients with proximal small intestinal mucosal disease (eg, celiac disease) cannot absorb the D-xylose in the intestine, and urinary and venous D-xylose levels will be low, as seen in this patient. By contrast, patients with malabsorption due to enzyme deficiencies (eg, chronic pancreatitis) will have normal absorption of D-xylose (Choice D). A false-positive D-xylose test (ie, low urinary D-xylose level despite normal mucosal absorption) can be seen in the following: Delayed gastric emptying Impaired glomerular filtration Small intestinal bacterial overgrowth (SIBO), characterized by alterations in small intestinal flora (due to abnormal intestinal anatomy or motility), leading to bacterial fermentation of the D-xylose before it can be absorbed. SIBO is treated with rifaximin; therefore, it is unlikely in this patient whose D-xylose test results did not change following treatment with rifaximin (Choice A). (Choice C) Intestinal lactase deficiency causes diarrhea, abdominal pain, and flatulence after consuming milk or milk-containing products. However, fecal fat and absorption of D-xylose will be normal. (Choice E) Crohn disease is characterized by transmural inflammation of the gastrointestinal tract, most commonly in the distal ileum. Patients may have steatorrhea due to abnormal absorption of bile salts in the distal ileum, but D-xylose is absorbed in the proximal small bowel and unlikely to be affected. Educational objective: D-xylose is a monosaccharide that is absorbed in the proximal small intestine without degradation by pancreatic or brush border enzymes. Patients with small intestinal mucosal disease will have impaired absorption of D-xylose. Patients with malabsorption due to enzyme deficiencies will have normal absorption of D-xylose.

A 45-Year-Old Man Comes to the Clinic for Evaluation of Chronic