ETIOPATHOGENESIS OF CHRONIC DIARRHEA
Chronic diarrhea is defined as the passage of loose stools lasting more than 2–4 weeks. Its etiopathogenesis can be categorized based on mechanism and etiology:
A. Based on Pathophysiologic Mechanisms
- Osmotic Diarrhea
- Caused by ingestion or malabsorption of osmotically active substances.
- Resolves with fasting.
- Examples:
- Lactase deficiency
- Disaccharidase deficiencies (e.g., sucrase-isomaltase)
- Congenital chloride diarrhea
- Secretory Diarrhea
- Due to increased active secretion or decreased absorption of electrolytes and water.
- Persists during fasting.
- Examples:
- Congenital chloride/bicarbonate diarrhea
- VIPoma
- Microscopic colitis
- Bile acid malabsorption
- Inflammatory Diarrhea
- Damage to intestinal mucosa leads to exudation of blood, mucus, protein.
- Examples:
- Inflammatory bowel disease (IBD)
- Cow’s milk protein allergy
- Infections (Giardia, TB)
- Dysmotility
- Altered intestinal motility affects absorption.
- Examples:
- Irritable bowel syndrome
- Post-infectious diarrhea
- Hyperthyroidism
- Malabsorptive Diarrhea
- From structural or functional loss of absorptive surface.
- Examples:
- Celiac disease
- Short bowel syndrome
- Abetalipoproteinemia
- Post-Infectious Diarrhea
- Following acute gastroenteritis.
- Can lead to transient lactose intolerance or persistent diarrhea.
B. Based on Etiological Classification
- Infectious
- Persistent infections: Giardia, Cryptosporidium, TB, HIV
- Allergic/Immunologic
- Cow’s milk protein allergy
- Food protein-induced enterocolitis
- IBD (Crohn’s, Ulcerative colitis)
- Celiac disease
- Malabsorptive Disorders
- Cystic fibrosis
- Celiac disease
- Bile acid deficiency
- Anatomic Abnormalities
- Short bowel syndrome
- Post-surgical states
- Endocrine and Metabolic Disorders
- Addison’s disease
- Hyperthyroidism
- VIPoma
- Functional/Non-organic
- Toddler’s diarrhea
- Irritable bowel syndrome
SCHEME OF INVESTIGATION FOR A CHILD WITH CHRONIC DIARRHEA
Step 1: Detailed History
- Duration, frequency, character of stools
- Failure to thrive, weight loss
- Blood/mucus in stool
- Dietary history (milk, gluten)
- Travel, contact history, pets
- Family history (CF, IBD, consanguinity)
Step 2: Physical Examination
- Nutritional status (height, weight, MUAC)
- Signs of malnutrition (wasting, vitamin deficiencies)
- Perianal findings (fistula, tags suggest Crohn’s)
- Systemic signs (thyromegaly, edema, clubbing)
Step 3: Baseline Laboratory Investigations
- CBC (anemia, eosinophilia)
- ESR/CRP (inflammation)
- Serum albumin, total proteins
- Electrolytes
- Stool microscopy, ova/cysts, culture
- Stool pH, reducing substances (suggest carbohydrate malabsorption)
- Stool fat estimation (Sudan stain or 72-hour fat test)
Step 4: Targeted Workup
Based on clinical suspicion:
| Condition Suspected | Specific Tests |
|---|---|
| Celiac Disease | Anti-TTG IgA, Total IgA |
| Cystic Fibrosis | Sweat chloride test, CFTR gene |
| IBD | Fecal calprotectin, colonoscopy with biopsy |
| Giardiasis | Stool antigen, ELISA, duodenal aspirate |
| Cow’s milk allergy | Stool eosinophils, elimination diet |
| Endocrinopathy | Thyroid function, cortisol |
| Malabsorption | Upper GI endoscopy, biopsy |
Step 5: Imaging and Endoscopy
- Abdominal USG/CT – mass, lymphadenopathy, bowel thickening
- Upper GI endoscopy with biopsy – celiac, eosinophilic gastroenteritis
- Colonoscopy with biopsy – IBD, TB
- Sweat test – CF
Step 6: Therapeutic Trials (in select cases)
- Lactose-free diet
- Elimination of cow’s milk protein
- Gluten-free diet trial (after testing)
- Empirical metronidazole for giardiasis
