What is the recommended evaluation and management for a patient with chronic diarrhea lasting at least four weeks?

Evaluation and Management of Chronic Diarrhoea

Definition and Initial Approach

Chronic diarrhoea is defined as the passage of ≥3 loose or liquid stools per day for more than 4 weeks and/or stool weight >200 g/day, and requires systematic evaluation starting with assessment for alarm features followed by first-line laboratory investigations and categorization by diarrhoea type. 1, 2

The 4-week duration threshold distinguishes chronic from acute diarrhoea and indicates a non-infectious aetiology requiring investigation. 2

History and Physical Examination

Alarm Features Requiring Urgent Evaluation

• Nocturnal diarrhoea (suggests organic disease rather than functional disorder) 3, 1
• Unintentional weight loss (excludes irritable bowel syndrome diagnosis) 3, 4
• Blood in stool 1
• Fever 1
• Recent onset (<3 months duration) 3

Critical Risk Factors to Identify

• Family history of colorectal cancer, inflammatory bowel disease, or coeliac disease 3, 1
• Medication review for diarrheogenic agents (magnesium products, NSAIDs, antibiotics, antihypertensives, theophyllines account for up to 4% of cases) 4
• Surgical history, particularly ileal resection, right colectomy, or gastric bypass 1
• Dietary triggers including wheat, dairy, coffee, high fructose/sorbitol intake 1

Distinguishing Diarrhoea Types by History

• Malabsorptive diarrhoea: bulky, malodorous, pale stools with steatorrhoea 3
• Inflammatory/colonic diarrhoea: liquid loose stools with blood or mucous 3
• Functional diarrhoea: intermittent symptoms, abdominal pain relieving with defecation, no nocturnal symptoms 3, 1

Critical pitfall: Rome criteria alone have only 52-74% specificity and miss 26-48% of organic disease including inflammatory bowel disease, microscopic colitis, and bile acid diarrhoea—all treatable conditions. 3, 1, 4

First-Line Investigations (Primary Care Setting)

Mandatory Initial Laboratory Tests

• Complete blood count 1, 4, 5
• C-reactive protein 1, 4, 5
• Electrolytes and basic metabolic panel 4, 5
• Liver function tests 1, 4
• Iron studies, vitamin B12, folate 1, 4
• Thyroid function tests 1, 4
• Anti-tissue transglutaminase IgA AND total IgA (to screen for coeliac disease; total IgA needed to exclude IgA deficiency) 1, 5
• Fecal calprotectin (distinguishes inflammatory from non-inflammatory causes) 1, 4

Categorization and Further Investigation

Age-Stratified Colonoscopy Approach

For patients ≥45-50 years OR any age with alarm features: Full colonoscopy with biopsies is mandatory. 1, 4

For patients <40-45 years without alarm features and normal fecal calprotectin: Flexible sigmoidoscopy may be sufficient, or colonoscopy can be deferred. 1

Critical pitfall: Always obtain colonic biopsies even with normal-appearing mucosa, as microscopic colitis can only be detected histologically and is a common, treatable cause. 1, 4

Categorizing by Diarrhoea Type

The British Society of Gastroenterology recommends categorizing diarrhoea as:

1. Inflammatory diarrhoea (elevated fecal calprotectin, blood/pus in stool)
2. Malabsorptive/fatty diarrhoea (steatorrhoea, weight loss, nutrient deficiencies)
3. Watery diarrhoea (secretory, osmotic, or functional) 3, 5, 6

Specific Conditions to Exclude

High-Priority Diagnoses

• Coeliac disease: Screened by anti-tissue transglutaminase IgA 1, 5
• Microscopic colitis: Requires colonic biopsies; affects older adults, particularly women 4
• Bile acid malabsorption: Consider SeHCAT scan or empiric trial of bile acid sequestrants (cholestyramine) 1, 4
• Colorectal neoplasia: Excluded by colonoscopy in appropriate age groups 3, 4
• Inflammatory bowel disease: Evaluated by fecal calprotectin and colonoscopy with biopsies 1, 4

Secondary Investigations for Persistent Undiagnosed Diarrhoea

• Small bowel bacterial overgrowth: Glucose or lactulose hydrogen breath test in patients with bloating, gas, and abdominal pain 1, 4
• Pancreatic insufficiency: Consider in appropriate clinical context 3
• Endocrine disorders: Thyroid function already obtained in first-line tests 4

Management Approach

Cause-Specific Treatment (Priority)

• Coeliac disease: Strict gluten-free diet 4
• Microscopic colitis: Budesonide 4
• Bile acid malabsorption: Cholestyramine 4
• Inflammatory bowel disease: Disease-specific therapy 4

Symptomatic Management

Loperamide is first-line pharmacologic therapy: Initial dose 4 mg, then 2 mg every 2-4 hours or after each unformed stool, maximum 16 mg daily. 4

Dietary modifications: Avoid spices, coffee, alcohol; reduce insoluble fiber intake. 4

Bile-sequestering agents: Alternative symptomatic option when loperamide insufficient. 7

Functional Diarrhoea/IBS-D Diagnosis

Irritable bowel syndrome with diarrhoea can only be diagnosed after excluding organic disease, particularly in patients without alarm features, with normal investigations, and meeting Rome criteria (abdominal pain ≥1 day/week for 3 months associated with 2 of: pain relief with defecation, change in stool frequency, change in stool form). 1

However, even with a 10-year duration and young age at onset suggesting functional disorder, targeted testing remains necessary to exclude microscopic colitis, bile acid diarrhoea, and inflammatory bowel disease. 1

Common Pitfalls to Avoid

• Never diagnose IBS in patients with weight loss—this is an exclusion criterion. 4
• Never skip colonic biopsies even with normal-appearing mucosa. 4
• Never rely on Rome criteria alone to exclude organic disease. 1, 4
• Never assume long symptom duration rules out organic disease—inflammatory bowel disease can smolder for years. 1
• Never forget to check total IgA when screening for coeliac disease, as IgA deficiency causes false-negative results. 5