WBR0467

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::Gastrointestinal
Prompt	[[Prompt::A 5-year-old male is brought by his mother to the physician's office concerned that he cannot drink milk. The patient's mother explains that whenever he drinks milk, the patient has explosive foul-smelling diarrhea and abdominal discomfort. Following appropriate work-up, endoscopy demonstrates normal gastrointestinal (GI) mucosa with no obvious abnormalities on biopsy. Which of the following most likely characterizes the type of diarrhea in this patient?]]
Answer A	[[AnswerA::Increase in fluid secretion in the small bowel lumen due to decreased absorption of electrolytes with stool osmolal gap < 50 mOsm/kg.]]
Answer A Explanation	[[AnswerAExp::Secretory diarrhea is frequently characterized by increased fluid secretion in the small bowel lumen, due to decreased absorption of electrolytes.]]
Answer B	AnswerB::Fecal fat output exceeding the absorptive capacity of the intestine
Answer B Explanation	AnswerBExp::Fatty diarrhea is characterized by fecal fat output exceeding the absorptive capacity of the intestine.
Answer C	AnswerC::Active solutes that obligate water retention in the intestinal lumen
Answer C Explanation	[[AnswerCExp::Osmotic diarrhea is characterized by the retention of water in the intestinal lumen, due to the presence of active solutes. In osmotic diarrhea, the stool osmolal gap is usually > 100 mOsm/kg.]]
Answer D	AnswerD::Enterocyte damage that cause mucosal disruption and abnormal absorption
Answer D Explanation	AnswerDExp::Inflammatory diarrhea is characterized by enterocyte damage, which causes mucosal disruption and abnormal absorption.
Answer E	AnswerE::Altered small intestinal motor activity
Answer E Explanation	AnswerEExp::Disordered motility may be a cause of diarrhea, characterized by a limited time for appropriate digestion to occur, in patients with hyperthyroidism or irritable bowel syndrome (IBS).
Right Answer	RightAnswer::C
Explanation	[[Explanation::The patient in this scenario presents with symptoms and signs that are consistent with lactase deficiency. Lactase deficiency is the most common type of disaccaridase deficiency, frequently associated with milk intolerance. Following milk ingestion, patients with lactase deficiency complain of abdominal pain, explosive foul smelling diarrhea, and headache. Lactase deficiency is also characterized by normal GI mucosa on biopsy. Lactase deficiency manifests with osmotic diarrhea due to the inability to absorb lactose, a compound containing osmotically active metabolites, in the intestinal lumen. This will drag water into the lumen, through osmosis, resulting in diarrhea. Taking a measurement of stool osmotic gap, aids in the differention of 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. Educational Objective: Lactase deficiency is a common cause of osmotic diarrhea, manifesting with lactose intolerance, abdominal pain, and explosive diarrhea following milk ingestion, with normal GI mucosa on endoscopy. References: Corinaldesi R, Stanghellini V, Barbara G, et al. Clinical approach to diarrhea. Intern Emerg Med. 2012;7(Suppl 3):S255-S262]]
Approved	Approved::Yes
Keyword	WBRKeyword::osmotic diarrhea, WBRKeyword::lactase deficiency, WBRKeyword::lactase, WBRKeyword::enzyme deficiency, WBRKeyword::diarrhea, WBRKeyword::disaccharide, WBRKeyword::enzymes, WBRKeyword::digestive system, WBRKeyword::excretory system
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