Diarrhoea

Definition
Diarrhoea is defined as the passage of loose, liquid stool. Urgency is the sensation of the need to defaecate without being able to delay. It may indicate rectal irritability but also occurs where the volume of liquid stool is too large, causing the rectum to be overwhelmed as a storage vessel. Frequency merely reflects the number of stools passed and may or may not be associated with urgency or diarrhoea.
KEY POINTS
• Bloody diarrhoea is always pathological and usually indicates colitis of one form or another.
• Infective causes are common in acute transient diarrhoea.
• In diarrhoea of uncertain origin, remember the endocrine causes.
• Consider parasitic infections in a history of foreign travel.
• Alternating morning diarrhoea and normal/pellety stools later in the day is rarely pathological.
• Diarrhoea developing in hospitalized patients may be due to Clostridium difficile infectionbcheck for CD toxin in the stool.
Important diagnostic features
Acute diarrhoea
Infections
• Shigella/Salmonella: associated colicky abdominal pain, vomiting.
• Dysentery: blood and mucus in motions, ulcers in rectum and Entamoeba histolytica in the stool, fever, sweating, tachycardia.
• Cholera: severe diarrhoea, ‘rice water’ stool, dehydration, history of foreign travel.
• Giardiasis.
Antibiotics
Short-lived, self-limiting, mild colicky pain.
Pseudomembranous colitis
Caused by Clostridium difficile infection, characterized by severe diarrhoea which may be bloody but occasionally acute constipation may indicate severe disease. Characteristic features on colonoscopy.
Chronic diarrhoea
Small bowel disease
• Crohn’s disease: diarrhoea, pain prominent, blood and mucus less common, young adults, long history, chronic malnourishment and weight loss.
• Coeliac disease: history of wheat and cereals intolerance, may present in adulthood with chronic diarrhoea and weight loss, abdominal pains.
• ‘Blind loop’ syndrome: frothy, foul-smelling liquid stool, due to bacterial overgrowth and fermentation, usually associated with previous surgery, may complicate Crohn’s disease.
Large bowel disease
• Ulcerative colitis: intermittent, blood and mucus, colicky pains, young adults. May be a short history in first presentations. Rarely presents with acute fulminant colitis with acute abdominal signs.
• Colon cancer: older, occasional blood streaks and mucus, change in frequency may be the only feature, positive faecal occult blood, rectal mass.
• Irritable bowel syndrome: diarrhoea and constipation mixed, bloating, colicky pain, small stool pellets, never blood.
• Spurious: impacted faeces in rectum, liquefied stool passes around faecal obstruction, elderly, mental illness, constipating drugs.
• Polyps (villous) (rare): watery, mucoid diarrhoea, K+ loss, commonest in rectum.
• Diverticular disease (rare).
Systemic disease
Thyrotoxicosis, anxiety, peptides from tumours (VIP, serotonin, substance P, calcitonin), laxative abuse.
KEY INVESTIGATIONS
• FBC: leucocytosis (infective causes, colitis), anaemia (colon cancer, ulcerative colitis, diverticular disease).
• Anti α-gliadin Abs: coeliac disease.
• Thyroid function tests: hyperthyroidism.
• Stool culture: infections (remember microscopy for parasites).
• Proctoscopy/sigmoidoscopy: cancer, colitis, polyps (simple, easy, cheap and safe; performed in outpatients).
• Flexible sigmoidoscopy: cancer, polyps, colitis, infections (relatively safe, well tolerated, high sensitivity).
• Colonoscopy: colitis (extent and severity), pseudomembranous colitis.
• Small bowel enema: Crohn’s disease, coeliac disease, Whipple’s disease.
• Faecal fat estimation/ERCP: pancreatic insufficiency.