Chronic Diarrhoea Diagnosis and Management

Categorization by Diarrhoea Type

The American Gastroenterological Association recommends categorizing diarrhoea by pathophysiologic mechanism, including watery, fatty, and inflammatory types, to guide targeted testing and narrow the differential diagnosis 1
Microscopic colitis accounts for 15% of chronic diarrhoea cases in older adults and has entirely normal-appearing mucosa on endoscopy but shows characteristic histologic changes only on biopsy 1
Bile acid malabsorption should be considered when colonoscopy is negative 1
Endocrine disorders, including hyperthyroidism, can cause secretory diarrhoea 2
Post-surgical states, including vagal nerve damage, gastric resection, or gut bypass, can reduce absorptive capacity and cause diarrhoea 3

Coeliac disease is the most common small bowel enteropathy in Western populations and typically results in weight loss and iron deficiency anaemia 4, 2
Small bowel bacterial overgrowth (SBBO) is more likely in patients with anatomical abnormalities such as dilation, diverticulosis, prior small bowel surgery, or pseudo-obstruction 4, 2
Giardiasis is a classic infectious malabsorptive cause 2
Pancreatic exocrine insufficiency from chronic pancreatitis or pancreatic carcinoma can cause malabsorptive diarrhoea 2
Crohn's disease or ulcerative colitis is characterized by blood and pus in stool and elevated fecal calprotectin 1
Clostridioides difficile colitis is a common cause of infectious diarrhoea, particularly in patients with recent antibiotic exposure 1

Nocturnal diarrhoea strongly indicates organic pathology rather than functional disorders and warrants expedited evaluation 5, 2, 1
Recent worsening of chronic symptoms suggests progressive organic disease requiring immediate evaluation 5, 1
Fecal incontinence during sleep indicates severe disease burden 1
Iron deficiency anaemia is a common complication of chronic diarrhoea and requires further investigation 4, 5

Post-surgical diarrhoea may be attributed to pyloric dysfunction, bile salt malabsorption, bacterial overgrowth, or gut bypass reducing absorptive capacity 3
Faecal incontinence may be the primary presenting symptom with underlying diarrhoea as the causative factor, particularly in patients with compromised sphincter complex from obstetric trauma, pelvic surgery, obesity, diabetes, or stroke 4, 3
Overflow diarrhoea from severe faecal loading occurs in patients with cognitive or behavioural issues, learning difficulties, or neurological/spinal disease 4, 3

The American College of Gastroenterology recommends not diagnosing IBS in patients with nocturnal diarrhoea, as this is an exclusion criterion for functional disorders 2, 1
Colonic biopsies should not be skipped even with normal-appearing mucosa, as microscopic colitis requires histologic diagnosis 2, 1
Unrecognised cases of coeliac disease are sometimes falsely diagnosed as diarrhoea-predominant IBS in colorectal clinics 4
CT imaging alone is inadequate for detecting microscopic colitis, early inflammatory bowel disease, or subtle mucosal abnormalities 1