Introduction
Diarrhoea affects millions globally, but understanding its cause—whether acute, chronic, infectious, or systemic—is crucial for effective diagnosis and treatment. This guide breaks down every possible type using diagrams, clinical reasoning, and evidence-based strategies.
What is Diarrhoea?
- Definition: passage of loose/liquid stools ≥3 times/day
- Associated symptoms: urgency, incontinence, bloating, cramping
- Differentiate with urgency, dysentery, steatorrhea
Types of Diarrhoea
1. Acute Diarrhoea
- Duration: <14 days
- Infective causes (viral, bacterial, protozoa)
- Antibiotic-associated: pseudomembranous colitis (C. difficile)
2. Chronic Diarrhoea
- Duration: >4 weeks
- Associated with IBS, IBD, coeliac disease, pancreatic insufficiency
- Alternating bowel habits in IBS
- Pale, foul-smelling stools in malabsorption
Causes of Diarrhoea by Site
Upper GI Tract
- Rapid gastric emptying
- Pancreatic exocrine insufficiency
- Cholestasis (bile salt deficiency → fat malabsorption)
Small Bowel Causes
- Coeliac disease: gluten-triggered enteropathy
- Crohn’s disease: segmental, transmural inflammation
- Whipple’s disease: malabsorption + weight loss
- Infective enteritis: viral, bacterial, parasitic
- Carcinoid, VIPoma: neuroendocrine tumors
- Resection of terminal ileum: bile salt diarrhea
Colonic Causes
- Ulcerative colitis: bloody diarrhoea, urgency
- Microscopic colitis: chronic watery diarrhoea
- C. difficile: greenish foul-smelling stools
- Colon cancer: intermittent, ± blood
- IBS: altered bowel habits, bloating
- Diverticular disease: intermittent with left lower quadrant pain
General/Systemic Causes
- Diabetes (autonomic neuropathy)
- Thyrotoxicosis (↑ motility)
- Uraemia
- Drug-induced (laxatives, metformin, antibiotics)
Pathophysiological Types of Diarrhoea
- Osmotic: lactose intolerance, sorbitol
- Secretory: cholera, VIPoma, bile salt malabsorption
- Inflammatory: IBD, infection
- Malabsorptive: coeliac, pancreatic insufficiency
- Motility-related: IBS, hyperthyroidism
Key Symptoms to Watch
- Blood in stool → colitis, cancer, dysentery
- Weight loss → IBD, malignancy, coeliac
- Steatorrhoea → pancreatic, bile salt, coeliac
- Night-time diarrhoea → organic, not IBS
- Fever → infection, IBD
- Foul odour + gas → blind loop, Whipple’s
Important Diagnostic Features
Infective Causes
- Viral: rotavirus, norovirus – short-lived watery
- Bacterial: E. coli, Shigella, Salmonella – bloody/mucoid
- Protozoal: Giardia, Entamoeba – chronic + travel history
Antibiotic-associated Diarrhoea
- Usually mild and self-limiting
- C. difficile: confirmed with stool toxin assay
- Treated with oral vancomycin or fidaxomicin
Chronic Diarrhoea Red Flags
| Symptom | Suggests |
|---|---|
| Blood in stool | Colitis, cancer |
| Weight loss | Malignancy, Crohn’s |
| Nocturnal diarrhoea | Organic pathology |
| History of surgery | Blind loop syndrome |
Key Investigations
| Test | Role |
|---|---|
| FBC | Anaemia (IBD, malignancy), leukocytosis (infection) |
| ESR/CRP | Inflammation in IBD |
| Stool studies | C. difficile toxin, culture, ova & parasite |
| Anti-tTG, anti-endomysial | Coeliac disease |
| Thyroid function test | Hyperthyroidism |
| Proctoscopy/sigmoidoscopy | Evaluate left-sided colitis, cancer |
| Colonoscopy | Full-length assessment, biopsies |
| Faecal elastase | Pancreatic insufficiency |
| Small bowel imaging | Crohn’s disease, lymphoma |
| ERCP/MRCP | Bile duct-related issues in fat malabsorption |
Management Principles
General Supportive Measures
- Hydration (oral/IV)
- Zinc supplementation
- Antimotility drugs (Loperamide – not in dysentery)
Cause-Specific Treatment
- Infection → antibiotics or antiparasitics
- IBD → steroids, 5-ASA, biologics
- Coeliac → lifelong gluten-free diet
- IBS → diet changes, psychological therapy
- Pancreatic insufficiency → enzyme supplements
FAQs
What is the difference between diarrhoea and dysentery?
Dysentery involves blood and mucus due to inflammation (usually colonic); diarrhoea may not.
Is IBS the same as chronic diarrhoea?
No—IBS has alternating patterns, normal investigations, and is a diagnosis of exclusion.
Why does coeliac disease cause diarrhoea?
Gluten-induced damage flattens villi, leading to fat and nutrient malabsorption.
What is the danger of prolonged diarrhoea?
Dehydration, electrolyte imbalance, weight loss, malnutrition.
Conclusion
Diarrhoea is not just an inconvenient symptom—it's often a sign of systemic or localized pathology. A structured clinical approach with timely investigations can differentiate harmless IBS from malignancy or IBD, guiding appropriate treatment and improved outcomes.
