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Definition - It is defined according to symptoms as increase in liquidity, frequency and volume of stools; and according to sign as increase in stool weight of more than 200gm/day.
Pseudo diarrhea - it is the frequent passage of small volume of stools. It is seen in irritable bowel syndrome and proctitis.
Classification - It is classified according to duration as
  1. Acute-Duration less than 2 weeks.
  2. Persistent-Duration of 2-4 weeks.
  3. Chronic-Duration of more than 4 weeks.
ACUTE DIARRHEA - 90% cases of acute diarrhea are due to infectious causes, rest 10% are due to noninfectious cause.
  1. Infectious causes-
    1. Toxin producer-
      1. Preformed toxin - Staphylococcus aureus, Bacillus cereus, Clostridium perfringens.Q
      2. Enterotoxin - Vibrio cholerae, ETEC, Klebsiella pneumoniae, Aeromonas sp.Q
      3. Enteroadherent-
      4. E.coli, Giardia,cryptosporadium,helminths
      5. Cytotoxin producers-
        Clostridium difficile, hemorrhagic E. coli.
      6. Invasive organisms-
        1) Minimal inflammation - Rotavirus, Norwalk virus
        2) Moderate inflammation - Salmonella, Campylobacter, Yersinia, Vibrio parahaemolyticus
        3) Severe inflammation - Shigella, enteroinvasive E. coli, Entamoeba histolytica. Q
  2. Non-infectious causes-
    1. Drug - Antibiotics, antiarrhythmic, laxatives, NSAIDs, antihypertensives, chemotherapeutic agents, antacids, Theophylline.
    2. Toxins - organophosphate insecticides, amanita mushroom, arsenic.
    3. Ischemia - Ischemic colitis.
    4. Diverticulitis - colonic diverticulitis.
    5. Graft vs host reaction.
Investigations - The most cases of acute diarrhea are self limiting and do not require detailed investigations. The indications for evaluation are-
  1. Profuse diarrhea with dehydration.
  2. Grossly bloody stools.
  3. ever>38.5 C.
  4. Duration >48 hrs without improvement.
  5. Age>50 years with severe abdominal pain.
  6. Immunocompromised pt.
  7. New community outbreak
Examination of the stools-
  1. Presence of WBCs in stools-bacteria, toxin, ischemic colitis.
  2. Occult blood in stools-colonic neoplasm, ischemia, ameobiasis, severe mucosal inflammation causing bacteria.
  3. Ova and cyst–for helminths
  4. Viral antigen-Rota virus
  5. Immunoassay for toxins-Clostridium difficileQ
  6. Protozoal antigen-Giardia, E. histolytica.Q
Endoscopy - If stool studies are unrevealing, flexible sigmoidoscopy with biopsy and upper GI endoscopy with duodenal aspirate and biopsy are indicated.
  1. Fluid and electrolyte replacement.
  2. Antimotility agents should be avoided in infectious diarrhea. They can be given in moderately severe nonfebrile, non bloody diarrhea.
  3. Antibiotics - The indications for the use of antibiotics are-
    1. Fever>38.5 C
    2. Bloody stools
    3. Increased in fecal WBCs
    4. Immunocompromised pt.
CHRONIC DIARRHEA - Most cases are due to non-infectious causes.
The main etiology are-
  1. Secretory - These are due to derangement in fluid and electrolyte transport across the enterocolic mucosa. They are characterized clinically by-
    1. Watery, large volume, painless stools.
    2. Diarrhea persists with fasting.
    3. No fecal osmotic gap.
The important causes are-
  1. Stimulant laxatives - senna, castor oil, bisacodyl
  2. Chronic alcohol ingestion - due to enterocyte injury with impaired sodium and water absorption and rapid transit time.
  3. Hormone-
    1. Carcinoid - due to release of intestinal secretagogues like serotonin, histamine, prostaglandin.
    2. Gastrinoma - due to marked volume overload to the small bowel, pancreatic enzyme inactivation by acid and damage of the intestinal epithelial surface by acid.
    3. VIPoma - due to vasoactive intestinal peptide.
    4. Medullary carcinoma of thyroid-due to calcitonin.
    5. Systemic mastocytosis - due to histamine release and intestinal filtration by mast cells.
    6. Colorectal villous adenoma - due to prostaglandin.
  4. Congenital defect in ion absorption - due to defective Cl/HCO3 exchange (congenital chloridorrhea) and defective Na/H exchange.
  5. Partial bowel obstruction - due to hypersecretion proximal to the obstruction site.
  6. Bowel resection/enterocolic fistula - due to inadequate surface for resorption of secreted fluids and electrolytes. Diarrhea worsen with eating.
  7. Bile acids - due to stimulation of colonic secretion.
  8. Addison’s disease
  1. Osmotic - It occurs due to osmotic active solute in the lumen which draw fluid in the lumen. Clinically these diarrhea stop with fasting. There is stool osmotic gap:290 -2 (Na+K) mosm/kg. The main causes are
    1. Osmotic laxatives-containing magnesium, phosphorus, sulfate.
    2. Lactase deficiency-due to osmotic active lactose.
    3. Non absorbable carbohydrates-sorbitol, lactulose.
  2. Steatorrhea - It is due to fat malabsorption with fecal fat excretion >6%. Clinically characterised by greasy, foul smelling and difficult to flush diarrhea.
    The main causes are-
    1. Intraluminal maldigestion-
      1. Pancreatic insufficiency - When 90% of pancreatic secretory functions are lost.
      2. Bacterial overgrowth syndrome - due to de conjugation of bile acids by the bacteria and altered micelle formation.
      3. Liver disease - cirrhosis and biliary obstruction causing deficient intraluminal bile acid concentration.
    2. Mucosal malabsorption-
      1. Celiac sprue (LQ 2012)
      2. Tropical sprue (LQ 2012)
      3. Whipple’s disease (LQ 2012) 
      4. Giardia (LQ 2012)
      5. Drugs
        i. Colchicine (inhibits crypt cell division and disaccharidase),
        ii. Cholestyramine (binds bile salts),
        iii. Neomycin (reduce crypt cell division, precipitates bile salts and micellar fatty acids, inhibits disaccharidases).
        iv. Abetalipoproteinemia-due to impaired chylomicron formation.
    3. Post mucosal lymphatic obstruction - due to
      1. Congenital intestinal lymphangiectasia
      2. Acquired lymphatic obstruction-due to trauma, tumor, infection.
  3. Inflammation-
    The diarrhea is due to exudation, fat malabsorption, disruption of fluid and electrolyte absorption, hypersecreting / hypermotility due to cytokines. Clinically it is characterised by pain, fever and bleeding. The important causes are-
    1. Inflammatory bowel diseases.
    2. Collagenous colitis.
    3. Eosinophilic gastroenteritis.
    4. Immunodeficiency.
    5. Radiation enterocolitis.
    6. Chronic graft vs host reaction.
    7. Beh|et’s syndrome.
  4. ​​Dysmotility-
    It is due to rapid transit time. The main causes are
    1. Hyperthyroidism-due to hyperphagia and rapid transit
    2. Diabetes-due to pancreatic insufficiency, autonomic neuropathy, bacterial overgrowth, rapid transit time.
    3. Visceral neuromyopathy
  5. Functional
    1. Munchausen syndrome
    2. Bulimia

Extra Edge


Pseudomembranous colitis: Nosocomial, cause by C. difficile, can be life threatening, may have infrequent loose stool to severe water diarrhea. No blood in stool, No tenderness on palpation.


Diagnosis: Sigmoidoscopy, Confirmation by presence of toxin in stool.


  1. Metronidazole
  2. Vancomycin
  3. Adjunctive therapy may include cholestyramine, a bile acid resin that can be used to bind C. difficile toxin.

Investigations of a case of diarrhea-
  1. Secretory diarrhea-Microbiological studies, biopsy, hormonal assay.
  2. Osmotic diarrhea-Stool Ph (low in lactase deficiency, high due to magnesium containing laxatives)
  3. Steatorrhea-Fecal fat estimation, small bowel biopsy, pancreatic function tests.
  4. Inflammatory diarrhea-Stool blood, leukocytes, microbiological study, colon sigmoidoscopy with biopsy.
  5. Dysmotility-Endocrinal functions.
  6. Factitial-suspect if stool osmolality decreased, with laxative abuse.
Treatment - Specific according to the etiology.


Recent Advances
  1. Alvimopan is use for constipation due to opioids and postoperative ileus. It is a new drug not given in Harrison’s 17th Edition.
  2. Aprepitant is a substance P/neurokinin NK-1 receptors antagonists. It is indicated for prevention of acute and delayed chemotherapy induced nausea and vomiting.

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