• Increased fluidity, frequency, or volume of stool output
  • Acute <2 wks           vs         Chronic >4 wks






Acute: Infection (most common is viral), medications (antibiotic-associated diarrhea; C.diff,  Magnesim containing antacids), malabsorption (lactose intolerance), ischemic bowel (elderly)

Chronic: IBS (most common), IBD, infection, medications, diverticulitis, colon ca, malabsorption syndromes (pancreatic insuff, celiac, short bowel syndrome, bacterial overgrowth), post-surgery (gastrectomy, vagotomy) endocrine (hyperthyroid, Addison’s ds, DM, gastrinoma\VIPoma)


Infectious causes:

» Staphylococcus: 1-6 hrs of ingestion

» Clostridium perfringens: enteritis necroticans

» coli: 5 types: enteropathogenic, enterotoxigenic, enteroaggregative, *enterohemorrhagic (associated with HUS and TTP), *enteroinvasive. *Cause bloody diarrhea

» Vibrio cholera: rice water stool, massive fluid loss

» Clostridium difficile: antibiotic associated (usually clindamycin), pseudomembranous colitis, treated by metronidazole, if recurs; retreat w\ metronidazole, if persists -> give vancomycin

» Yersinia enterocolitis: bloody diarrhea, terminal ileitis, mesenteric lymphadenitis (mimics appendicitis)

» Campylobacter: bloody diarrhea, most common, post-infec complication: Guillain-Barré syndrome

» Salmonella: bloody diarrhea, risk in achlorhydra (because acid sensitive)

» Shigellosis: bloody diarrhea, tenesmus, Hemolytic-uremic syndrome



CBC w\ diff, renal and liver function, electrolytes, bacterial culture, ova\parasite, colonoscopy, biopsy (to confirm celiac), TSH, fecal lactoferrin (if neg -> rule out inflammatory causes), osmotic gap (>40 is osmotic diarrhea, <50 is secretory), fecal PH (acidic ->sugar malabsorption ‘lactose intolerance’ or laxatives), stool phenolphthalein (for laxative abuse), D-Xylose test (bacterial overgrowth), hydrogen breath test (lactose intolerance), CT (if IBD or diverticulitis)



Rehydration and replace electrolytes, treat underlying cause, antibiotics if infectious cause, loperamide (anti diarrheal)



Random notes:

  • IBS: chronic or intermittent diarrhea (classically alternates w\ constipation), or flare-up during stressful periods
  • Persistent, frothy, foul-smelling diarrhea -> pancreatic or small-bowel cause
  • Foul-smelling, watery, explosive diarrhea w\ mucus -> giardiasis (traveler’s diarrhea)
  • Nocturnal diarrhea almost always -> organic cause
  • Blood on surface of stool or toilet paper -> anal origin (hemorrhoid, fissure)
  • Small bowel diarrhea -> large volume
  • Large bowel diarrhea -> small volume
  • Osmotic diarrhea improves with fasting, unlike secretory
  • Diarrhea causes metabolic acidosis w\ hypokalemia


Download the PDF version: here


  • The Johns Hopkins Internal Medicine Board Review
  • Davidson’s Principles and Practice of Medicine

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