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For further information, see CMDT Part 15-06: Diarrhea

Key Features

Essentials of Diagnosis

  • Diarrhea present for > 4 weeks

  • Before embarking on extensive work up, common causes should be excluded, including medications, chronic infections, and irritable bowel syndrome

  • Classification

    • Medications

    • Osmotic diarrhea

    • Secretory conditions

    • Inflammatory conditions

    • Malabsorption conditions

    • Motility disorders

    • Chronic infections

    • Systemic disorders

General Considerations

  • 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 resolve during fasting

  • Secretory diarrhea is caused by increased intestinal secretion or decreased absorption with little change in stool output during fasting

  • The major causes of malabsorption are small intestinal mucosal diseases, intestinal resections, lymphatic obstruction, small intestinal bacterial overgrowth, and pancreatic insufficiency

  • Motility disorders are secondary to systemic disorders, radiation enteritis, or surgery that lead to rapid transit or to stasis of intestinal contents with bacterial overgrowth, malabsorption

  • Immunocompromised patients are susceptible to Microsporidia, Cryptosporidium, cytomegalovirus, Isospora belli, Cyclospora, and Mycobacterium avium-intracellulare infections

  • Chronic systemic conditions such as thyroid disease, diabetes, and collagen vascular disorders may cause diarrhea through alterations in motility or intestinal absorption


  • Lactase deficiency

    • Occurs in 75% of nonwhite adults and 25% of whites

    • May be acquired with viral gastroenteritis, medical illness, or gastrointestinal surgery

Clinical Findings

Symptoms and Signs

  • Osmotic diarrheas

    • Abdominal distention

    • Bloating

    • Flatulence due to increased colonic gas production

  • Secretory diarrhea

    • High-volume (> 1 L/day) watery diarrhea

    • Dehydration

    • Electrolyte imbalance

  • Inflammatory conditions

    • Abdominal pain

    • Fever

    • Weight loss

    • Hematochezia

  • Malabsorption syndromes

    • Weight loss

    • Osmotic diarrhea

    • Steatorrhea

    • Nutritional deficiencies

Differential Diagnosis

  • Common

    • Irritable bowel syndrome

    • 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

    • Inflammatory bowel disease

    • Cancer with obstruction and pseudodiarrhea

    • Radiation colitis

  • 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

    • Reduced bile salts: ileal resection, Crohn disease, postcholecystectomy

  • Motility disorders

    • Irritable bowel syndrome

    • Postsurgical: vagotomy, partial gastrectomy, blind loop with bacterial overgrowth

    • Systemic disease: diabetes mellitus, hyperthyroidism, scleroderma

    • Caffeine or alcohol use

  • Chronic infections

    • Parasites: giardiasis, amebiasis, strongyloidiasis


Laboratory Tests

  • Obtain complete blood count, serum electrolytes, liver biochemical tests, calcium, phosphorus, albumin, thyroid-stimulating hormone

  • Prothrombin time/INR, erythrocyte sedimentation rate, and C-reactive protein should be obtained in most patients

  • Serologic testing for celiac disease with the IgA tissue transglutaminase antibody ...

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