Chronic diarrhea

Chronic diarrhea is defined as ≥3 loose stools per day for >4 weeks. The differential clusters into: (1) osmotic — lactose intolerance, fructose malabsorption, magnesium-containing laxatives; resolves with fasting; (2) secretory — bile-acid diarrhoea (post-cholecystectomy or ileal disease), microscopic colitis, hormonal (VIPoma, carcinoid); does NOT resolve with fasting; (3) inflammatory — IBD (Crohn's, ulcerative colitis), celiac disease, infectious (Clostridioides difficile, parasitic, tuberculosis), microscopic colitis; with blood, mucus, urgency, abdominal pain; (4) fatty (steatorrhoea) — pancreatic insufficiency, cholestasis, small bowel disease, bacterial overgrowth; pale, greasy, foul-smelling stool that floats; (5) functional — IBS-diarrhoea predominant; pattern related to stress, food triggers, no nocturnal symptoms or weight loss. Alarm features that require investigation: nocturnal stools, weight loss, anaemia, blood in stool, family history of colorectal cancer or IBD, onset after age 50.

• IBS-diarrhoea predominant — by far commonest; daytime pattern, no alarm features.
• Lactose / fructose intolerance — food-related; symptom-free on elimination.
• Celiac disease — chronic with bloating, weight loss, iron-deficiency anaemia, dermatitis herpetiformis.
• Inflammatory bowel disease (Crohn's, UC) — blood, urgency, nocturnal stools, weight loss, raised CRP.
• Bile-acid diarrhoea — post-cholecystectomy or after ileal resection; nocturnal urgency.
• Microscopic colitis — older women, watery, NSAID/PPI/SSRI associated; normal colonoscopy + biopsy diagnoses.
• Chronic pancreatitis — steatorrhoea, abdominal pain, often alcohol-related.
• Hyperthyroidism — soft frequent stools + weight loss + tremor + palpitations.
• Clostridioides difficile — post-antibiotic, hospital exposure, recurrent.
• Colorectal cancer — new symptoms after age 50, family history, blood in stool.

Baseline for chronic diarrhoea: full blood count (anaemia of IBD or coeliac), CRP + ESR (raised in IBD, normal in IBS), albumin (low in malabsorption / protein-losing enteropathy), ferritin + B12 + folate (deficient with malabsorption), TSH (hyperthyroidism), coeliac serology (anti-tissue-transglutaminase + total IgA), stool studies — calprotectin (excellent IBS-vs-IBD discriminator), C. diff toxin if any antibiotic exposure, ova-and-parasites if travel/immunosuppression. Faecal elastase for suspected pancreatic insufficiency. Colonoscopy + biopsies if alarm features, age >50, persistent symptoms, raised calprotectin, or family history of colorectal cancer / IBD. Mediora.AI surfaces the iron / B12 / TSH / coeliac pattern; the diagnostic decision is gastroenterology.