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Probability diagnosis


  • Gastroenteritis/infective enteritis

  • Dietary indiscretion

  • Antibiotic reaction


  • Irritable bowel syndrome (IBS)

  • Drug reactions (e.g. laxatives)

  • Chronic infections

Serious disorders not to be missed


  • colorectal cancer

  • ovarian cancer

  • peritoneal cancer


  • cholera

  • typhoid/paratyphoid

  • amoebiasis

  • malaria

  • enterohaemorrhagic E. coli enteritis

  • HIV infection (AIDS)


Inflammatory bowel disease:

  • Crohn/ulcerative colitis

  • pseudomembranous colitis


Pelvic appendicitis/pelvic abscess

Pitfalls (often missed)

Coeliac disease

Faecal impaction with spurious diarrhoea

Lactase deficiency

Giardia lamblia infection

Cryptosporidium infection

Malabsorption states (e.g. coeliac disease)

Vitamin C and other oral drugs

Nematode infections:

  • strongyloides (threadworm)

  • whipworm

  • hookworm



Post-GIT surgery

Ischaemic colitis (elderly)


  • Addison disease

  • carcinoid tumours

  • short bowel syndrome

  • amyloidosis

  • toxic shock

  • Zollinger–Ellison syndrome

Masquerades checklist


Drugs (see list)


Is the patient trying to tell me something?

Yes, diarrhoea may be a manifestation of anxiety state or irritable bowel syndrome.

Key history

Establish what the patient means by diarrhoea. Analyse the nature of the stools, frequency, associated symptoms (e.g. abdominal pain) and constitutional symptoms such as fever and weight loss. Drug history, travel history and family history.

Key examination

  • Focus on the general state (esp. of severe gastroenteritis), the abdomen, rectum and skin

  • Ideally the stool should be examined (note the presence of blood, mucus or steatorrhoea)

Key investigations

In some instances such as acute self-limiting diarrhoea nil is required. Consider:

  • microscopy and culture of stool

  • FBE


  • C. difficile tissue culture assay

  • U&E

  • specific tests for organisms

  • endoscopy

  • selective radiology (e.g. small bowel enema).

Diagnostic tips

  • Giardiasis (profuse bubbly diarrhoea) is more common than realised.

  • Remember spurious diarrhoea and the rectal examination in the elderly.

  • IBS rarely causes nocturnal diarrhoea but causes recurrent pain in the right hypochondrium.

  • Some drugs that can cause diarrhoea: alcohol, antibiotics, digoxin, colchicine, cytotoxic agents, H2-receptor antagonists, iron compounds, laxatives, metformin, sildenafil, statins, thyroxine.

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