WBR0467
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| 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 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 characterized by an increase in 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 rention 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 that cause 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 that is characterized by a limited time for appropriate digestion to occur, as seen in patients with hyperthyroidism or irritable bowel syndrome (IBS). |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The patient in the vignette presents with symptoms and signs that are most consistent with lactase deficiency. Lactase deficiency is the most common type of disaccaridase deficiency that is characterized by intolerate to 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 causes osmotic diarrhea because patients will not be able to absorb lactose, a compound that contains osmotically active metabolites, in the intestinal lumen which will drive water into the lumen and cause diarrhea. To differentiate osmotic diarrhea from secretory diarrhea, measurement of stool osmotic gap is helpful. In osmotic diarrhea, stool osmolal gap is usually greater than 100 mOsm/kg; whereas secretory diarrhea is associated with stool osmolal gap usually less than 50 mOsm/kg. Educational Objective: Lactase deficiency is a common cause of osmotic diarrhea that is characterized by milk intolerance and symptoms of abdominal pain and explosive diarrhea following milk ingestion with normal GI mucosa on endoscopy. Reference:
Corinaldesi R, Stanghellini V, Barbara G, et al. Clinical approach to diarrhea. Intern Emerg Med. 2012;7(Suppl 3):S255-S262 |
| Approved | Approved::No |
| Keyword | WBRKeyword::osmotic, WBRKeyword::diarrhea, WBRKeyword::lactase, WBRKeyword::deficiency, WBRKeyword::lactase deficiency, WBRKeyword::osmotic diarrhea, WBRKeyword::disaccaride |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |