What is the diagnostic and treatment approach for a patient presenting with chronic diarrhea?

Diagnostic and Treatment Algorithm for Chronic Diarrhea

The diagnostic approach to chronic diarrhea should follow a systematic, stepwise algorithm that begins with categorization of diarrhea type, followed by targeted testing and treatment based on the most likely underlying causes. 1

Definition and Initial Assessment

Chronic diarrhea is defined as:

• Passage of loose stools lasting >4 weeks
• ≥3 loose stools per day
• Stool weight >200g/day

Primary Care Evaluation

1. Detailed clinical history focusing on:

   • Duration and pattern of symptoms
   • Stool characteristics (watery, fatty, bloody)
   • Nocturnal symptoms (suggests organic disease)
   • Weight loss (suggests malabsorption or inflammatory conditions)
   • Travel history
   • Medication use
   • Previous surgeries (especially GI tract)
   • Family history of GI disorders
   • Dietary factors (lactose, fructose, sorbitol intake)
   • Alcohol consumption

2. Initial laboratory testing:

   • Full blood count
   • C-reactive protein
   • Ferritin
   • Thyroid function tests
   • Anti-tissue transglutaminase IgA and total IgA (for celiac disease)
   • Basic metabolic panel
   • Fecal calprotectin (to screen for inflammatory bowel disease) 1
   • Stool tests for Giardia (using antigen detection or PCR) 1

Categorization of Chronic Diarrhea

1. Watery Diarrhea

• Secretory: Persists with fasting, large volume
• Osmotic: Improves with fasting, normal volume
• Functional: Associated with pain relieved by defecation

2. Fatty Diarrhea (Malabsorption)

• Steatorrhea, weight loss, nutritional deficiencies

3. Inflammatory Diarrhea

• Blood, pus in stool, elevated inflammatory markers

Secondary Care Evaluation

When initial testing is inconclusive or symptoms are severe, refer for specialized testing:

Colonoscopy Indications:

• Age >45 years
• Alarm features (weight loss, blood in stool, nocturnal symptoms)
• Elevated fecal calprotectin
• Family history of colorectal cancer

Additional Testing Based on Suspected Category:

For Watery Diarrhea:

• SeHCAT scan or empiric trial of bile acid sequestrants for suspected bile acid malabsorption
• Colonoscopy with biopsies for microscopic colitis
• Endocrine workup (if systemic symptoms suggest)

For Fatty Diarrhea:

• Duodenal biopsies (even with negative celiac serology)
• Fecal elastase for pancreatic insufficiency
• Small bowel imaging

For Inflammatory Diarrhea:

• Stool cultures and C. difficile testing
• Colonoscopy with biopsies

Special Considerations

Infectious Causes

• Test for ova and parasites only with travel history to high-risk areas 1
• Consider C. difficile testing in patients with antibiotic exposure 1
• HIV testing in appropriate risk groups 1

Small Bowel Bacterial Overgrowth

• Consider in patients with previous surgery, diabetes, or systemic sclerosis
• Hydrogen breath tests or empiric antibiotic trial 1

Treatment Approach

1. Treat specific identified causes:

   • Celiac disease: Gluten-free diet
   • Inflammatory bowel disease: Anti-inflammatory medications
   • Microscopic colitis: Budesonide
   • Bile acid malabsorption: Bile acid sequestrants
   • Pancreatic insufficiency: Enzyme replacement
   • Bacterial overgrowth: Targeted antibiotics

2. Symptomatic treatment:

   • Loperamide for control of symptoms (initial dose 2-4 mg, up to 16 mg/day) 2
   • Diphenoxylate/atropine for refractory cases (initial dose two tablets four times daily) 3
   • Clinical improvement should be observed within 48 hours for acute causes and within 10 days for chronic causes 3

3. Dietary modifications:

   • Low FODMAP diet for suspected functional diarrhea
   • Lactose restriction if lactose intolerance suspected
   • Avoidance of caffeine, alcohol, and sorbitol

When to Refer to Gastroenterology

• Alarm features (weight loss, blood in stool, nocturnal symptoms)
• Abnormal initial laboratory findings
• Symptoms persisting despite empiric treatment
• Need for endoscopic evaluation
• Suspected inflammatory bowel disease or celiac disease

Common Pitfalls to Avoid

1. Overlooking medication-induced diarrhea - Always review all medications including OTC supplements
2. Missing celiac disease - Test for IgA deficiency when celiac serology is negative but suspicion is high
3. Inadequate stool testing - Single samples may miss pathogens; consider multiple specimens
4. Premature diagnosis of IBS - Ensure adequate exclusion of organic disease before diagnosing functional disorders
5. Failure to recognize microscopic colitis - Common in older patients with watery diarrhea; requires colonic biopsies

By following this systematic approach, most cases of chronic diarrhea can be accurately diagnosed and effectively treated, improving patient quality of life and preventing complications from untreated disease.