II. Causes: Osmotic Diarrhea

  1. Findings: fecal osmotic gap >125 mOsm/kg
  2. Malabsorption
    1. Lactose malabsorption (Lactose Intolerance)
    2. Fructose malabsorption
    3. Glucose malabsorption
    4. Galactose malabsorption
    5. Gluten-sensitive Enteropathy (Celiac Sprue)
  3. Magnesium
    1. Magnesium Sulfate (Laxatives)
    2. Magnesium antacids
    3. Magnesium Laxatives
  4. Excessive High sugar juice intake
    1. Apple juice
    2. Pear juice
  5. Sugar Alcohols
    1. Mannitol ingestion
    2. Sorbitol ingestion (chewing gum Diarrhea)
    3. Xylitol
  6. Laxatives
    1. Sodium phosphate
    2. Sodium citrate
    3. Lactulose therapy
    4. Sodium Sulfate (Glauber's Salt)

III. Causes: Secretory Diarrhea

  1. Findings: Large volume stools (>1 L/day, persists at night and with Fasting)
  2. Drug-Induced Diarrhea
  3. Secretory villous adenoma of Rectum
  4. Small Bowel total villous atrophy
  5. Intestinal Lymphoma
  6. Bile acid malabsorption
  7. Chronic infections (granulomatous)
  8. Pseudopancreatic Cholera Syndrome
  9. Alcoholism
  10. Non-Osmotic Laxatives (e.g. senna, Docusate)
  11. Post-operative changes
    1. Cholecystectomy
    2. Gastrectomy
    3. Vagotomy
    4. Ileocolic resection
  12. Inflammatory Bowel Disease
    1. Usually inflammatory Diarrhea
    2. Crohn's Disease
    3. Ulcerative Colitis
    4. Microscopic Colitis (Lymphocytic Colitis, Collagenous collitis)
    5. Diverticulitis
  13. Endocrine Causes
    1. Hyperthyroidism
    2. Medullary Thyroid Carcinoma
    3. Islet Cell Tumor
      1. Gastrinoma (Zollinger-Ellison Syndrome)
      2. Vipoma (Watery Diarrhea, Hypokalemia, achlorhydria)
    4. Malignant Carcinoid syndrome
    5. Mastocytosis
    6. Pheochromocytoma
  14. Collagen Vascular Disease
    1. Systemic Lupus Erythematosus
    2. Scleroderma
    3. Mixed connective tissue disease

IV. Causes: Functional Diarrhea

  1. Findings: Small volume (<350 ml/day) watery stools, better at night and with Fasting
  2. Irritable Bowel Syndrome

V. Labs

  1. Fecal electrolytes (fecal sodium, fecal potassium)
    1. Electrolytes increased in Secretory Diarrhea
      1. Electrolytes negligible in Osmotic Diarrhea
    2. Small osmotic gap <50 mOsm/kg in Secretory Diarrhea
  2. Stool pH
    1. pH <6 in carbohydrate malabsorption

VI. Evaluation

  1. Osmotic Diarrhea: Fecal osmotic gap >125 mOsm/kg
    1. If Fasting improves Diarrhea, consider breath hydrogen test for Lactose Intolerance (or empiric avoidance)
  2. Secretory Diarrhea: Fecal osmotic gap <50 mOsm/kg
    1. Obtain stool tests (Ova and Parasites, Giardia, culture and sensitivity, specific infections)
    2. Colonoscopy
    3. Obtain TSH, ACTH
    4. Consider testing for Carcinoid, Gastrinoma, Pheochromocytoma, mastocytosis
    5. Consider autoimmune labs (e.g. ANA)
  3. Functional Diarrhea: Fecal osmotic gap normal
    1. Trial on empiric Irritable Bowel Syndrome management (dietary modification)
    2. If no improvement, test for Celiac Sprue

VII. References

  1. Schiller in Feldman (2002) Sleisenger GI, p. 136

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