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For further information, see CMDT Part 17-06: Diarrhea
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Essentials of Diagnosis
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Diarrhea present for > 4 weeks
Before embarking on extensive work-up, common causes should be excluded, including medications, chronic infections, and irritable bowel syndrome (IBS)
Classification
Medications
Osmotic diarrheas
Secretory conditions
Inflammatory conditions
Malabsorption conditions
Motility disorders
Chronic infections
Systemic disorders
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General Considerations
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Medications that can commonly cause diarrhea include
Cholinesterase inhibitors
Selective serotonin reuptake inhibitors
Angiotensin II-receptor blockers
Proton pump inhibitors
Nonsteroidal anti-inflammatory drugs
Metformin
Allopurinol
Orlistat
Osmotic diarrheas
Secretory diarrhea
Caused by increased intestinal secretion or decreased absorption
There is little change in stool output during fasting
Causes include endocrine tumors, bile salt malabsorption, and microscopic colitis
Inflammatory conditions
Diarrhea present in most patients with irritable bowel disease (ulcerative colitis, Crohn disease)
Abdominal pain, fever, weight loss, hematochezia also may be present
Malabsorptive conditions
Major causes: small intestinal mucosal diseases, intestinal resections, lymphatic obstruction, small intestinal bacterial overgrowth, and pancreatic insufficiency
Characteristics: weight loss, osmotic diarrhea, steatorrhea, and nutritional deficiencies
Significant diarrhea in the absence of weight loss is not likely to be due to malabsorption
Motility disorders
IBS most common cause of chronic diarrhea in young adults; should be considered in patients with lower abdominal pain and altered bowel habits without evidence of organic disease
Abnormal intestinal motility also may be secondary to systemic disorders, radiation enteritis, or surgery
Immunocompromised patients are susceptible to Microsporidia, Cryptosporidium, cytomegalovirus, Isospora belli, Cyclospora, and Mycobacterium avium-intracellulare infections
Chronic systemic conditions such as thyroid disease, diabetes mellitus, and collagen vascular disorders may cause diarrhea through alterations in motility or intestinal absorption
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Lactase deficiency
Occurs in 75% of non-White adults and 25% of Whites
May be acquired with viral gastroenteritis, medical illness, or gastrointestinal surgery
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Osmotic diarrheas
Secretory diarrhea
Inflammatory conditions
Abdominal pain
Fever
Weight loss
Hematochezia
Pus may be present
Malabsorption syndromes
Weight loss
Osmotic diarrhea
Malodorous stool
Steatorrhea
Nutritional deficiencies
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Differential Diagnosis
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Common
IBS
Parasites
Caffeine
Laxative abuse
Osmotic
Lactase deficiency
Medications: antacids, lactulose, sorbitol, olestra
Factitious: magnesium-containing antacids or laxatives
Secretory
Hormonal: Zollinger-Ellison syndrome (gastrinoma), carcinoid, VIPoma, medullary thyroid carcinoma, adrenal insufficiency
Laxative abuse: cascara, senna
Medications
Microscopic colitis
Inflammatory conditions
Malabsorption
Small bowel: celiac disease, Whipple disease, tropical sprue, eosinophilic gastroenteritis, small bowel resection, Crohn disease
Lymphatic obstruction: lymphoma, carcinoid, tuberculosis, M avium-intracellulare infection, Kaposi sarcoma, sarcoidosis, retroperitoneal fibrosis
Pancreatic insufficiency: chronic pancreatitis, cystic fibrosis, pancreatic cancer
Bacterial overgrowth, eg, diabetes mellitus
Reduced ...