WBR0468

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology, MainCategory::Pharmacology
Sub Category	SubCategory::Gastrointestinal
Prompt	[[Prompt::A 5-year-old boy is brought by his mother to the physician's office because she is concerned that he is unable to ingest dairy products anymore. She explains that every time he attempts to drink milk, he experiences abdominal pain and explosive diarrhea. Following appropriate work-up, the boy is diagnosed with lactase deficiency. Which cause of diarrhea is most likely characterized by the same type of diarrhea associated with lactase deficiency?]]
Answer A	AnswerA::Administration of lactulose
Answer A Explanation	AnswerAExp::Administration of lactulose induces osmotic diarrhea.
Answer B	AnswerB::Carcinoid tumor
Answer B Explanation	AnswerBExp::Carcinoid tumors frequently manifest with secretory diarrhea.
Answer C	AnswerC::Rectal villous adenoma
Answer C Explanation	AnswerCExp::Rectal villous adenoma frequently manifests with secretory diarrhea.
Answer D	AnswerD::Administration of selective serotonin reuptake inhibitors (SSRI)
Answer D Explanation	AnswerDExp::SSRI administration may manifest with secretory diarrhea.
Answer E	AnswerE::Laxative abuse
Answer E Explanation	AnswerEExp::Laxative abuse frequently manifests with secretory diarrhea.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Lactase deficiency (hypolactasia) is the most common type of disaccharidase deficiency that is associated with milk intolerance. Lactase deficiency is common among North American, European, and Australian populations. The enzyme lactase-phloizin hydrolase (lactase) is a beta-galactosidase that hydrolyzes lactose to glucose plus galactose before they are absorbed by the intestinal enterocytes into the blood. The enzyme is normally present on the apical surface of enterocytes along the brush border of the small intestine, especially in the mid-jejunum. The activity of lactase is at its peak at birth and decreases gradually with age. Following milk ingestion, patients with lactase deficiency complain of abdominal pain, bloating, explosive foul-smelling diarrhea, and occasionally, headaches. Lactase deficiency manifests with osmotic-type diarrhea due to patients' inability to absorb lactose, a compound containing osmotically active metabolites, in the intestinal lumen. Metabolites drag water into the lumen, through osmosis, resulting in diarrhea. Accordingly, measurements of stool osmotic gap is a clinical test that helps physicians distinguish osmotic diarrhea from secretory diarrhea. In osmotic diarrhea, the stool osmolal gap is usually greater than 100 mOsm/kg; whereas secretory diarrhea is associated with a stool osmolal gap less than 50 mOsm/kg. Lactulose, a synthetic disaccharide, is undigested by human enterocytes. Lactulose-induced diarrhea manifests with a a similar mechanism to that of lactase deficiency-induced diarrhea. Since lactulose is not absorbed by the small intestine, the osmotically active compounds drive water into the intestinal lumen and cause osmotic diarrhea. Educational Objective: Lactulose is a synthetic disaccharide that is not digested by human enterocytes. Ingestion of lactulose results in osmotic-type diarrhea, similar to that of lactase deficiency. References: Clausen MR, Mortensen PB. Lactulose, disaccharides, and colonic flora. Drugs. 1997;53(6):930-942. First Aid 2014 page 353, 372]]
Approved	Approved::Yes
Keyword	WBRKeyword::Lactulose, WBRKeyword::Osmotic diarrhea, WBRKeyword::Lactase deficiency, WBRKeyword::Lactulose, WBRKeyword::Types of diarrhea, WBRKeyword::Lactose intolerance
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