see also:

• diarrhoea
• Clinical Gastroenterology and Hepatology 2017: Chronic Diarrhea: Diagnosis and Management (pdf)

• Chronic diarrhoea is defined by duration of >4 weeks
• 5% will develop an episode of chronic diarrhoea some time in their life
• Failure to make a diagnosis is more likely due to overlooking a common cause than missing a rare cause of chronic diarrhoea
• Specific dietary components may cause or aggravate chronic diarrhea. A careful dietary history is essential
• True food allergies are rare causes of chronic diarrhea in adults
• Many drugs cause diarrhea - careful review of current medications is essential
• pelvic irradiation can cause chronic diarrhea, sometimes starting years after exposure.
• tuberculosis (TB) of GIT is a rare cause ¹⁾
• Whipple's disease is a rare cause and is associated with polyarthralgias ²⁾

• No objective evidence of diarrhea
  • Change in stool frequency, intermittent diarrhea, faecal incontinence, treatment with antidiarrheal drugs during collection
• Hyperdefecation
  • Possible IBS, proctitis, abnormal rectal reservoir function
• Abnormal consistency (unformed to runny stools)
  • Possible IBS
• Elevated fecal osmotic gap
  • Presumed mild carbohydrate malabsorption or excess Mg intake from supplements
• Steatorrhea
  • Malabsorption or maldigestion

• Secretory diarrhea without steatorrhea
  • Microscopic colitis or other cause of secretory diarrhea
• Carbohydrate malabsorption without steatorrhea (high fecal osmolal gap)
  • Ingestion of poorly absorbed carbohydrates, malabsorption
• Steatorrhea with or without carbohydrate malabsorption
  • Small bowel mucosal disease, pancreatic insufficiency, SIBO, bile acid deficiency
• Osmotic diarrhea
  • Ingestion of poorly absorbed ions (eg, magnesium, phosphate, sulfate) or osmotically active polymers (eg, polyethylene glycol)
• Blood or pus in stool
  • suggests inflammatory causes of diarrhea such as inflammatory bowel disease (IBD)

• Bile acid malabsorption
• Carbohydrate malabsorption
• Chronic idiopathic secretory diarrhea
• Fecal incontinence
• hyperthyroidism - may cause paradoxic weight gain if it also causes congestive cardiac failure as in thyroid storm
• Functional diarrhea
• Iatrogenic diarrhea (drugs, surgery, radiation)
• IBS
• Microscopic colitis
• Autonomic neuropathy
• Pancreatic exocrine insufficiency
• Peptide-secreting tumors
• SIBO
• Surreptitious laxative ingestion

• FBE
• U&E
• LFTs - check for low albumin to suggest malabsorption
• TSH - hyperthyroidism
• CRP - raised in Crohn's disease especially, but only mildly elevated in ulcerative colitis
• stool m/c/s for parasites, etc
  • stool tests can be used to categorize diarrhoea and should be considered when the diagnosis remains obscure after initial assessment.
• patients without alarm features who meet criteria for IBS should be treated without further testing
• fecal calprotectin - non-specific marker of bowel inflammation
• consider colonoscopy with mucosal biopsy, esp. if inflammatory and secretory diarrhoea
  • valuable for diagnosing microscopic colitis, IBD, neoplasia, and other inflammatory conditions.
• if unexplained steatorrhoea, upper GIT endoscopy with biopsies of duodenum and jejunum
  • duodenal aspiration for Giardia
• consider:
  • hydrogen breath test
    • malabsorption of carbohydrates and SIBO
  • new tests being developed for bile acid malabsorption (BAM) which may account for half of IBS cases
  • pancreatic function testing is difficult
• NB. hormone-secreting tumors are rare causes of secretory diarrhoea and most positive tests end up being false-positive results.

• patients who meet criteria IBS without alarm features (eg. inflammatory features) can be treated as per irritable bowel syndrome (IBS)
• opiate antidiarrheals are a mainstay of symptomatic management when specific treatment is not possible. Dosing should be scheduled rather than as needed.
• Octreotide is used to treat diarrhea in patients with carcinoid syndrome or VIPomas, chemotherapy-induced diarrhea, HIV, and dumping syndrome after gastric surgery.
• Clonidine, an a2-adrenergic agonist drug that simulates absorption and slows intestinal transit, is used for diabetic diarrhea that is due to a loss of noradrenergic innervation. It also may be useful in the diarrhea of opiate withdrawal.
• Anticholinergic medications used to treat other conditions may mitigate diarrhea. For example, tricyclic antidepressants used to manage depression or pain may treat coexisting diarrhea.
• For small volume watery diarrhea and fecal incontinence, fiber supplementation or a hydrophilic, poorly fermentable colloid (calcium polycarbophil, carboxymethylcellulose) sometimes may be helpful.
• Oral calcium supplementation may treat mild chronic diarrhea.
• Bismuth may be effective in the treatment of microscopic colitis.
• Alosetron is a serotonin type 3 antagonist that slows colonic transit and increases fluid absorption. It is useful in diarrhea-predominant IBS and functional diarrhea, but because of a risk of colonic ischemia and severe constipation, it is used infrequently.
• Crofelemer, a chloride channel antagonist, is approved for the treatment of HIV-associated diarrhea