Chronic diarrhoea
A structured approach to causes, investigations, and management
What is chronic diarrhoea?
Chronic diarrhoea lasts 4 weeks or longer. It is rarely infectious and requires systematic evaluation.
Major categories of chronic diarrhoea
1. Inflammatory causes
Examples: IBD, microscopic colitis, chronic infections (C. diff), colorectal cancer. Clues: blood/mucus, nocturnal diarrhoea, weight loss, anaemia, raised markers.
2. Malabsorptive causes
Examples: coeliac disease, pancreatic exocrine insufficiency, bile acid diarrhoea, short bowel. Clues: greasy stools, bloating, deficiencies, weight loss.
3. Functional disorders
Examples: IBS-D, post-infectious IBS. IBS is a diagnosis of exclusion.
4. Endocrine and hormonal causes
Examples: hyperthyroidism, gastrinoma, VIPoma, medication-related effects.
5. Post-surgical causes
Examples: post-cholecystectomy bile acid diarrhoea, post-pancreatectomy malabsorption, dumping syndrome.
6. Medication-related diarrhoea
Common culprits: metformin, PPIs, antibiotics, magnesium supplements, SSRIs, chemotherapy/immunotherapy.
Baseline investigations
- Full blood count
- Inflammatory markers
- Electrolytes
- LFTs
- Coeliac serology
- Stool studies where appropriate
Red flags
Urgent investigation for bleeding, significant weight loss, iron deficiency anaemia, nocturnal symptoms, family history, onset after age 50.
Key takeaway: Chronic diarrhoea requires a calm, structured approach. Most causes are identifiable and many are treatable.