Guideline-Based Classification of Chronic Diarrhoea
According to the British Society of Gastroenterology guidelines, chronic diarrhoea should be classified using a multi-tiered approach that distinguishes between organic versus functional causes, followed by anatomical/pathophysiological categorization into colonic, small bowel, pancreatic, endocrine, and miscellaneous causes. 1
Primary Classification Framework
The initial classification distinguishes:
1. Organic vs. Functional Diarrhoea
- Organic diarrhoea presents with alarm features: duration <3 months, nocturnal or continuous symptoms, significant weight loss, blood or mucus in stool 2, 1
- Functional diarrhoea typically shows intermittent symptoms >3 months, absence of alarm features, and meets Rome criteria (though specificity is only 52-74%) 2
2. Stool Characteristic Classification
This practical approach helps narrow the differential immediately:
- Malabsorptive pattern: Bulky, malodorous, pale stools with steatorrhoea (though milder forms may appear normal) 2
- Colonic/inflammatory/secretory pattern: Liquid loose stools with blood or mucous discharge 2
Anatomical/Etiological Classification System
The guidelines provide a comprehensive anatomical framework 2:
Colonic Causes
- Colonic neoplasia
- Ulcerative and Crohn's colitis
- Microscopic colitis
Small Bowel Causes
- Coeliac disease
- Crohn's disease
- Other enteropathies (Whipple's disease, tropical sprue, amyloid, intestinal lymphangiectasia)
- Bile acid malabsorption
- Disaccharidase deficiency
- Small bowel bacterial overgrowth
- Mesenteric ischaemia
- Radiation enteritis
- Lymphoma
- Giardiasis and chronic infections
Pancreatic Causes
- Chronic pancreatitis
- Pancreatic carcinoma
- Cystic fibrosis
Endocrine Causes
- Hyperthyroidism
- Diabetes
- Hypoparathyroidism
- Addison's disease
- Hormone-secreting tumours (VIPoma, gastrinoma, carcinoid)
Other Causes
- Factitious diarrhoea (laxative abuse—represents 20% of tertiary referral cases) 2
- Surgical causes (small bowel resections, internal fistulae)
- Drug-induced (up to 4% of cases) 2
- Alcohol
- Autonomic neuropathy
Contemporary Five-Category System
More recent literature proposes a simplified five-category classification that better reflects clinical practice 3, 4:
- Drug side effect
- Postoperative
- Postinfectious
- Malabsorptive
- Inflammatory
- Functional
This system emphasizes common, treatable causes first before pursuing rare diagnoses.
Critical Clinical Pitfalls
The most important caveat: Up to 20% of patients referred to tertiary centers have factitious diarrhoea from laxative abuse, making it the most common cause of previously undiagnosed chronic diarrhoea 2. Always maintain clinical suspicion, particularly in patients with extensive negative workups, psychiatric history (especially eating disorders), or healthcare profession connections.
Duration matters for classification: While chronic diarrhoea is defined as >4 weeks duration 2, 5, symptoms <3 months are more likely organic, while >3 months with intermittent pattern suggests functional etiology 2, 1.
The 2018 BSG guidelines emphasize that classification should guide investigation strategy rather than being purely academic—distinguishing malabsorptive from inflammatory patterns immediately narrows your diagnostic testing pathway 1.