What is the approach to diagnosing and managing chronic diarrhea?

Diagnostic Approach to Chronic Diarrhea

A systematic approach to chronic diarrhea (≥3 loose stools daily for >4 weeks) should begin with categorizing the diarrhea type as watery, fatty, or inflammatory, followed by targeted testing based on clinical suspicion to determine the underlying cause and guide appropriate treatment. 1

Initial Assessment

Definition and Classification

• Chronic diarrhea is defined as abnormal passage of ≥3 loose stools per day for more than 4 weeks 1
• Distinguish between true diarrhea and fecal incontinence, which patients often misinterpret as diarrhea 1

Primary Care Evaluation

• Take a detailed history to establish whether symptoms are organic vs. functional, distinguish malabsorptive from colonic/inflammatory forms, and identify specific causes 1
• Look for alarm features: nocturnal diarrhea, weight loss, blood in stool, recent onset (<3 months), and persistent symptoms 1
• Perform initial screening tests: complete blood count, C-reactive protein, electrolytes, liver function tests, iron studies, vitamin B12, folate, thyroid function, and celiac serology (anti-tissue transglutaminase IgA and total IgA) 1, 2
• Stool tests should be performed if infectious etiology or inflammatory component is suspected 1

Key Historical Elements

Risk Factors to Assess

• Family history of neoplastic, inflammatory bowel, or celiac disease 1
• Previous surgery, especially involving the ileum, right colon, or gastric bypass (can lead to bile acid malabsorption or bacterial overgrowth) 1
• Previous pancreatic disease 1
• Systemic diseases: thyroid disorders, diabetes mellitus, adrenal disease, systemic sclerosis 1
• Alcohol consumption (direct toxic effect on intestinal epithelium, decreased pancreatic function) 1
• Dietary factors: excessive caffeine, sorbitol, fructose, or lactose in lactase-deficient individuals 1
• Medication review: antibiotics (risk of C. difficile), laxatives, metformin, etc. 2

Diagnostic Algorithm

Step 1: Categorize Diarrhea Type

• Watery diarrhea: Includes secretory, osmotic, and functional types 2

  • Functional disorders (IBS, functional diarrhea) - most common
  • Secretory causes: bile acid malabsorption, microscopic colitis, endocrine disorders
  • Osmotic causes: carbohydrate malabsorption, laxative abuse

• Fatty diarrhea: Indicates malabsorption or maldigestion 2

  • Celiac disease, giardiasis, pancreatic exocrine insufficiency
  • Characterized by steatorrhea, excess gas, weight loss

• Inflammatory diarrhea: Suggests inflammatory bowel disease or infection 2

  • IBD (Crohn's disease, ulcerative colitis)
  • Infections (C. difficile, invasive bacteria/parasites)
  • Colorectal cancer
  • Characterized by blood, pus in stool, elevated fecal calprotectin

Step 2: Targeted Testing Based on Suspected Category

For Suspected Inflammatory Diarrhea

• Fecal calprotectin to exclude colonic inflammation, especially in those under 40 with IBS symptoms 1
• Stool culture for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC in appropriate clinical scenarios 1
• Colonoscopy with biopsies of right and left colon (not just rectum) to exclude microscopic colitis 1

For Suspected Malabsorptive/Fatty Diarrhea

• Celiac disease serology (anti-tissue transglutaminase IgA) 1, 2
• If lactose maldigestion is suspected, hydrogen breath testing or trial of lactose withdrawal 1
• Fecal elastase testing for pancreatic insufficiency 1
• Small bowel imaging with MR enterography for small bowel abnormalities 1
• Video capsule endoscopy for assessing small bowel abnormalities 1

For Suspected Watery Diarrhea

• SeHCAT testing or serum bile acid precursor 7α-hydroxy-4-cholesten-3-one for bile acid diarrhea 1
• Colonoscopy with biopsies to exclude microscopic colitis 1
• Glucose hydrogen breath test for small bowel bacterial overgrowth 1

Step 3: Special Considerations

For Persistent Unexplained Diarrhea

• Consider rare causes such as hormone-secreting tumors (VIPomas) when high-volume watery diarrhea persists after excluding common causes 1
• Consider empiric trials of therapy (antibiotics for suspected bacterial overgrowth, bile acid sequestrants for suspected bile acid malabsorption) 1

For Immunocompromised Patients

• Broader testing for organisms including Cryptosporidium, Cyclospora, Cystoisospora, microsporidia, Mycobacterium avium complex, and cytomegalovirus 1

Management Principles

• Treat the underlying cause when identified 3
• For symptomatic management when specific cause is not treatable:
  • Loperamide for non-inflammatory diarrhea (caution: avoid in inflammatory or infectious diarrhea) 4, 3
  • Cholestyramine for bile acid diarrhea 3
  • Rifaximin may be considered for IBS with diarrhea (550 mg three times daily for 14 days) 5
  • Bulking agents and probiotics for functional diarrhea 3

Common Pitfalls to Avoid

• Failing to distinguish between functional disorders and organic disease 1
• Overlooking microscopic colitis, which can present similar to IBS but requires different treatment 1
• Missing bile acid malabsorption, which is common but often underdiagnosed 1
• Treating with antibiotics without confirmed infection, which can increase risk of C. difficile and antimicrobial resistance 5
• Inadequate colon biopsies (sampling only rectum) when microscopic colitis is suspected 1