Definition. Loose stools with or without increased stool frequency persisting for more than 4 weeks.

Etiology: 

Infection. Giardiasis, amebiasis, Clostridium difficile, Cryptosporidium

Whipples disease, caused by Tropheryma whippleii, is a unique cause of diarrhea. Begins as a nondeforming arthritis in middle age, which may be manifest for years before GI symptoms begin. The illness progresses to include abdominal pain, diarrhea, weight loss, fever, lymphadenopathy, and occasionally CNS symptoms. Diagnosis is by biopsy of the small intestine yielding the offending organism.

Inflammation. Ulcerative colitis, Crohns disease, ischemic colitis, diverticulitis, AIDS-related chronic diarrhea, collagenous colitis (very common in middle-aged and elderly women), microscopic (lymphocytic) colitis.

Drugs. Laxatives, antibiotics, NSAIDs, magnesium-containing antacids, alcohol.

Malabsorption. Short bowel syndrome, celiac sprue (gluten sensitive enteropathy), carbohydrate malabsorption, pancreatic insufficiency, bacterial overgrowth.

Endocrine. Hypothyroidism or hyperthyroidism, diabetes, adrenal insufficiency, hypoparathyroidism, Zollinger-Ellison syndrome.

Motility disorders. Irritable bowel syndrome, dumping syndrome.

Infiltrative disorders. Amyloidosis, diffuse intestinal lymphoma, scleroderma.

Hormone-producing tumors. VIPoma, carcinoid tumor, pheochromocytoma, ganglioneuroma, villous adenoma, medullary thyroid carcinoma or systemic mastocytosis.

Others. Fecal incontinence, food allergy, radiation enteritis or colitis.

Most patients with chronic watery diarrhea and abdominal pain have no identifiable cause for diarrhea except for irritable bowel syndrome.

Evaluation

History. Inquire about diurnal variation, relationship to meals, weight loss, and character of stools (such as foul-smelling or greasy stools characteristic of malabsorption or chronic bloody stools and abdominal pain or tenesmus suggestive of inflammatory bowel disease or tumor). Absence of stools at night suggests (but does not prove) a non-organic etiology.

Physical examination. Look for abdominal tenderness, distension, organomegaly, anal fistulas, rectal mass, and hyperactive bowel sounds.

Laboratory analyses.

1. CBC with differential. Anemia is suggestive of chronic blood loss, infection, malabsorption, or neoplasm. Eosinophilia may be secondary to parasitic disease or allergic reaction. Megaloblastic anemia may result from vitamin B₁₂ or folate malabsorption.
2. ESR, C-reactive protein. If elevated, may indicate chronic inflammation.
3. Serum electrolytes, magnesium, iron, renal function, albumin, cholesterol. Calcium, phosphate, and alkaline phosphatase levels to evaluate for parathyroid disease. A fasting or random glucose can be used to screen for diabetes. Carotene levels may be low because of fat malabsorption. PT/PTT may be abnormal because of decreased vitamin K absorption. Thyroid function abnormalities should be ruled out. Hypocalcemia may be due to vitamin D malabsorption.
4. Stool exam for occult blood, leukocytes, and ova and parasites. A stool specimen should be sent for culture and sensitivity; one culture is sufficient. Stool antigen test (sensitivity 92%, specificity 98%) is available for Giardia organisms and is more sensitive than an "O & P." The same type of test is available for Cryptosporidium. Generally 3 stools are sent of ova and parasites.
5. Special tests.
   1. A 72-hour fecal fat quantitation or Sudan staining of stool if steatorrhea (fat malabsorption) is suspected.
   2. d-Xylose absorption (decreased in disorders of proximal small intestine).
   3. A stool pH <5.3 is diagnostic of a carbohydrate intolerance. Breath hydrogen test for lactase deficiency. Can also check for reducing substances in stool or therapeutic trial of lactose-free diet.
   4. Small intestinal biopsy (useful for Whipples disease, celiac sprue, regional enteritis, some parasitic infestations).
   5. Smooth muscle endomysial antibody titers may be positive in celiac sprue/gluten insensitivity. Tissue transglutaminase is starting to be utilized as an alternative test (see Sprue below).
   6. Small bowel culture for bacterial overgrowth.
   7. Stool test with phenolphthalein (test for factitious laxative abuse). Bring stool pH to 8.0. If the specimen turns maroon in color, this indicates the presence of phenolphthalein, an ingredient in over-the-counter laxative products. Urine tests are available to detect aloes, senna alkaloids, and bisacodyl.
   8. Sigmoidoscopy should be done to detect inflammation of the colon or rectum, neoplasms, and parasites.
   9. Radiographic studies. Plain abdominal radiography and barium studies of the upper GI tract, small intestine, and colon.

Treatment

Should be directed toward underlying cause of the chronic diarrhea.

Occasionally, when a definitive diagnosis cannot be made, one might empirically try:

Dietary restriction. Restricting lactose, gluten, or long-chain fatty acids in the diet. Restrictions should be done systematically so that if symptoms improve, the restricted factor can be identified and removed permanently from the diet. Lactase replacements (such as Lactaid caplets) are available OTC for patients intolerant to lactose.

Pancreatic enzyme supplementation (Creon [pancrelipase] capsules) for suspected pancreatic exocrine deficiency (such as cystic fibrosis, chronic pancreatitis).

Increase dietary or supplemental fiber.

Cholestyramine, which tends to have a constipating effect.

Antimicrobials (such as metronidazole).

Judicious use of antidiarrheal medication may be appropriate for symptomatic relief in some patients. Avoid opiates in the treatment of chronic diarrhea. See acute diarrhea section for dosages and cautions.