Differentials
Crohn's disease
SIGNS / SYMPTOMS
May present with fatigue, diarrhoea, abdominal pain, weight loss, fever and rectal bleeding.
Other signs may include oral ulcers, perianal skin tags, fistulae, abscesses and sinus tracts; abdominal exam may reveal a palpable mass in the ileocaecal area; no mass present on digital rectal examination.
INVESTIGATIONS
Stool culture, microscopy and antigen testing: negative.
Faecal occult blood: positive.
Upper gastrointestinal and small bowel series: oedema and ulceration of the mucosa with luminal narrowing and strictures.
CT/MRI abdomen: skip lesions, bowel wall thickening, surrounding inflammation, abscess, fistulae.
Colonoscopy: aphthous ulcers, hyperaemia, oedema, cobblestoning, skip lesions.
Ulcerative colitis
SIGNS / SYMPTOMS
May present with bloody diarrhoea, history of lower abdominal pain, faecal urgency, presence of extraintestinal manifestations (e.g., erythema nodosum, acute arthropathy), history of primary sclerosing cholangitis. No mass present on digital rectal examination.
INVESTIGATIONS
Stool culture, microscopy and antigen testing: negative.
Histology: continuous distal disease, mucin depletion, basal plasmacytosis, diffuse mucosal atrophy, absence of granulomata and anal sparing.
Colonoscopy: rectal involvement, continuous uniform involvement, loss of vascular marking, diffuse erythema, mucosal granularity, normal terminal ileum (or mild 'backwash' ileitis in pancolitis).
Microscopic colitis
SIGNS / SYMPTOMS
Chronic watery, non-bloody diarrhoea.
Other common symptoms include faecal urgency, faecal incontinence, and nocturnal stools.
More common in patients >50 years and female.
INVESTIGATIONS
Ileocolonoscopy with biopsies from the right and left colon: confirms diagnosis.[48] Colonic mucosa has a normal or near-normal gross appearance.
Biopsy: demonstrates collagenous colitis (i.e., thickened subepithelial collagenous band of ≥10 micrometre (normal <5 micrometre) or lymphocytic colitis (i.e., increased number of intraepithelial lymphocytes of ≥20 per 100 surface epithelial cells (normal <5 micrometre). Both types show an increased inflammatory infiltrate in the lamina propria.[48]
Coeliac disease
SIGNS / SYMPTOMS
Patients with coeliac disease usually have weight loss. The physical examination is usually normal. Some patients with coeliac disease will have early osteoporosis.
INVESTIGATIONS
Basic laboratory tests: may show iron-deficiency anaemia, hypocalcaemia, or a prolonged prothrombin time, although many patients with coeliac disease will have no routine laboratory abnormalities.
Anti-tissue transglutaminase antibodies may be detected in coeliac disease.[44] Small bowel biopsy will be abnormal with partial villous atrophy in coeliac disease.
Colon cancer
SIGNS / SYMPTOMS
Colon cancer can sometimes cause a change in bowel habits with either constipation or more frequent, smaller calibre stools. Some, but not all, colon cancer patients will have blood in their stool, and a rectal cancer may be palpable on rectal examination.
INVESTIGATIONS
FBC: iron-deficiency anaemia may be present.
Faecal occult blood: may be positive.
Quantitative faecal immunochemical test (FIT): The UK guidelines recommend urgent referral to secondary care for FIT value of ≥10 micrograms of haemoglobin/g of faeces.
Endoscopy: will demonstrate malignant growth; colon cancer can be diagnosed by colonoscopy, whereas cancers of the rectum, sigmoid, and lower descending colon can be seen with flexible sigmoidoscopy.
Barium enema: although less sensitive than endoscopy, many colon cancers can be seen on air-contrast barium enema.
CT colonography is an option for screening for colorectal cancer.
Bowel infections
SIGNS / SYMPTOMS
Most bacterial and viral infections in immunocompetent patients are acute. The parasite Giardia can be associated with diarrhoea, nausea, and bloating. Giardiasis may also cause steatorrhoea.
INVESTIGATIONS
Stool examination positive for ova and parasites or stool antigen detection positive for G lamblia can be used for screening. Multiple stools should be examined.
Non-coeliac gluten sensitivity
SIGNS / SYMPTOMS
Patients will have bloating, abdominal cramping, and diarrhoea similar to IBS.
INVESTIGATIONS
Studies will be negative, including tissue transglutaminase antibody.
There is no biomarker.
Patient's symptoms improve on gluten-free diet, especially without wheat.[49]
Bile acid malabsorption
SIGNS / SYMPTOMS
Patients have persistent diarrhoea. May be clinically indistinguishable from diarrhoea-predominant IBS (IBS-D). More than 25% of patients who meet the diagnostic criteria for IBS-D have bile acid malabsorption.[30]
INVESTIGATIONS
Test result indicating bile acid malabsorption: elevated faecal bile acids on 48-hour stool collection; reduced serum fibroblast growth factor 19; <15% retained 23‐seleno‐25‐homotaurocholic acid (SeHCAT) 1 week after ingestion.
Symptoms improve with an empiric trial of bile acid binder.
Small bowel bacterial overgrowth
SIGNS / SYMPTOMS
Patients present with abdominal bloating, diarrhoea, and abdominal cramps. History may show conditions that alter intestinal anatomy, motility, and gastric acid secretion (e.g., use of proton pump inhibitors or anatomical disturbances in the bowel, including fistulae, diverticula, and blind loops created after surgery).[50]
INVESTIGATIONS
Hydrogen breath testing indicates bacterial overgrowth.
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