Differentials
Infectious gastroenteritis
SIGNS / SYMPTOMS
Recent travel or exposure. Often acute, may be associated with fever or other systemic symptoms.
INVESTIGATIONS
Microscopic examination of the stool for ova and parasites: may isolate specific ova and/or parasites, including Giardia and Entamoeba histolytica.
Osmotic diarrhoea
SIGNS / SYMPTOMS
Symptoms resolve with fasting.
INVESTIGATIONS
Contrast-enhanced intestinal radiographs: helps differentiate from intestinal hypermotility and inflammatory bowel disease.
Biopsy rules out infectious causes as well as inflammatory bowel disease.
Ileal bile acid malabsorption
SIGNS / SYMPTOMS
Lower volume of stool output. Symptoms resolve with fasting.
INVESTIGATIONS
Cholestyramine trial: binding of excess bile salts reduces the diarrhoea that is typically a symptom of excess bile reaching the colon.
Gastrinoma
SIGNS / SYMPTOMS
Acidic diarrhoea, increased gastric acid production, gastro-oesophageal reflux disease, pain/peptic ulcer disease, absence of metabolic acidosis.
INVESTIGATIONS
Serum gastrin levels: raised.
Carcinoid syndrome
SIGNS / SYMPTOMS
More severe flushing.
INVESTIGATIONS
24-hour urinary 5-hydroxyindoleacetic acid: raised.
Somatostatinoma
SIGNS / SYMPTOMS
Steatorrhoea, diabetes mellitus, gallstones.
INVESTIGATIONS
Plasma somatostatin levels: raised.
Crohn's disease
SIGNS / SYMPTOMS
Less severe diarrhoea and associated abdominal pain. Perianal lesions, mouth ulceration, blood in stools.
INVESTIGATIONS
Plain film abdominal radiograph: small-bowel or colonic dilatation, calcification, sacroiliitis, and/or intra-abdominal abscesses.
Colonoscopy: aphthous ulcers, hyperaemia, oedema, cobblestoning, and/or skip lesions.
Biopsy: transmural involvement with non-caseating granulomas.
Ulcerative colitis
SIGNS / SYMPTOMS
Less severe diarrhoea and associated abdominal pain. Rectal bleeding, blood in stools, arthritis, spondylitis, skin rash, uveitis, episcleritis.
INVESTIGATIONS
Plain film abdominal radiograph: ulcerated colon usually contains no solid faeces, dilated loops with air-fluid level secondary to ileus.
Colonoscopy and flexible sigmoidoscopy: continuous uniform rectal involvement, loss of vascular marking, diffuse erythema, mucosal granularity, fistulas, and/or mild 'backwash' ileitis in pancolitis.
Biopsy: continuous distal disease, mucin depletion, basal plasmacytosis, diffuse mucosal atrophy, absence of granulomata, and anal sparing.
Irritable bowel syndrome (IBS)
SIGNS / SYMPTOMS
Often presents with intermittent and chronic history of diarrhoea. Less severe diarrhoea and associated abdominal pain.
INVESTIGATIONS
No specific diagnostic test; symptoms and age guide initial work-up to exclude non-IBS disease.
Coeliac disease
SIGNS / SYMPTOMS
Diarrhoea and evidence of malabsorption are typical.
INVESTIGATIONS
Immunoglobulin A-tissue transglutaminase (IgA-tTG) or IgG DGP (deamidated gliadin peptide): raised titre.
Endoscopy with duodenal biopsy: atrophy and scalloping of mucosal folds, nodularity and mosaic pattern of mucosa, typical histological findings (presence of intra-epithelial lymphocytes, villous atrophy, and crypt hyperplasia).
Small intestinal bacterial overgrowth
SIGNS / SYMPTOMS
History of diabetes, past surgery, coeliac or Crohn's disease; typical symptoms are bloating, wind, flatulence, cramping, and mild to moderate diarrhoea.
Examination is generally non-specific.
INVESTIGATIONS
Breath test: rise of >20 ppm of hydrogen or methane (or both) within 90 minutes.
Therapeutic trial of antibiotics: significant and lasting improvement of symptoms.
Colon carcinoma
SIGNS / SYMPTOMS
Less severe diarrhoea and improvement with fasting. Rectal bleeding, positive family history, anaemia.
INVESTIGATIONS
Quantitative faecal immunochemical test: ≥10 micrograms of haemoglobin/g of faeces.
Colonoscopy: ulcerating exophytic mucosal lesion that may narrow the bowel lumen.
Biopsy: characteristic pathological appearances and degree of tumour differentiation.
Drug effects
SIGNS / SYMPTOMS
Long-term laxative abuse; other diarrhoea-causing drugs (e.g., proton-pump inhibitors, non-steroidal anti-inflammatory drugs, metformin, quinine); in many cases, patients on multiple drugs; time of onset can be very variable, so can be difficult to pinpoint offending agent.
INVESTIGATIONS
Improvement in symptoms upon discontinuation of drug.
Hyperthyroidism
SIGNS / SYMPTOMS
Less severe diarrhoea. Palpitations, menstrual irregularity, tremor, anxiety, diaphoresis, exophthalmos.
INVESTIGATIONS
Thyroid function testing: reduced thyroid-stimulating hormone, raised triiodothyronine, and raised thyroxine.
Addison's disease
SIGNS / SYMPTOMS
Systemic collapse, hyperpigmentation, salt craving.
INVESTIGATIONS
Serum electrolyte levels: reduced serum sodium, reduced serum calcium, raised potassium.
Adrenocorticotropic hormone level: raised.
Medullary cancer of the thyroid
SIGNS / SYMPTOMS
Neck mass, family history of multiple endocrine neoplasia type 2A or 2B.
INVESTIGATIONS
Serum calcitonin levels: may be raised.
Biopsy: characteristic pathological appearances.
Phaeochromocytoma
SIGNS / SYMPTOMS
Hypertension, palpitations, diaphoresis.
INVESTIGATIONS
Urinary or serum catecholamine, metanephrine, normetanephrine levels: raised.
Neuroblastoma
SIGNS / SYMPTOMS
Rarely occurs over the age of 10 years.
INVESTIGATIONS
Serum and/or urinary catecholamine levels: may be raised.
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