2. Crohn's disease is a chronic inflammatory bowel
disease (IBD) of unknown aetiology, characterised by focal,
asymmetrical, transmural and occasionally granulomatous
inflammation. Infectious agents such as Mycobacterium
paratuberculosis, Pseudomonasspp. and Listeria spp. have all
been implicated. An increase in TNF-alpha, high-fat diets and
genetic mutations have all been mooted as possible causes.
It may affect any part of the gastrointestinal tract but particularly
the terminal ileum and proximal colon.
Disease is restricted to the small bowel in 30% of patients and the
large bowel in 30% of patients. 40% of patients have involvement
of the small and large bowel.
Fistulae and strictures may occur.
3. SYMPTOMS
Symptoms are variable but often include diarrhoea (which may be bloody and
become chronic - ie present for more than six weeks), abdominal pain and/or weight
loss. Such symptoms should raise the suspicion of Crohn's disease, especially in
patients of young age.
Typically, there will be periods of acute exacerbation, interspersed with remissions or
less active disease.
Systemic symptoms of malaise, anorexia, or fever are common.
The history should include enquiry about possible extra-intestinal manifestations
involving the mouth, skin, eyes, joints and episodes of perianal abscess or anal
fissure.
Children may present with poor growth, delayed puberty, malnutrition and bone
demineralisation.
General ill health with signs of weight loss, fluid depletion and anaemia.
There may be hypotension, tachycardia and pyrexia during acute exacerbations.
Abdominal tenderness or distension, palpable masses.
Anal and perianal lesions (pendulous skin tags, abscesses, fistulae) are
characteristic., Mouth ulcers.
Clubbing, erythema nodosum, pyoderma gangrenosum.
Conjunctivitis, episcleritis, iritis., Large joint arthritis, sacroiliitis (10-12%), ankylosing
spondylitis.
Fatty liver, primary sclerosing cholangitis (rare), cholangiocarcinoma (rare).
Granulomata may occur (in 50-70% of patients) in the skin, epiglottis, mouth, vocal
cords, liver, nodes, mesentery, peritoneum, bones, joints, muscle or kidney.
Renal stones., Osteomalacia., Malnutrition., Amyloidosis.
4. INVESTIGATIONS
The diagnosis is confirmed by clinical evaluation and a combination of endoscopic,
histological, radiological and biochemical investigations.
Initial investigations are FBC, CRP, U&Es, LFTs, stool culture and microscopy. Serum
levels of CRP are useful for assessing a patient's risk of relapse. High CRP levels are
indicative of active disease or a bacterial complication. CRP levels can be used to guide
therapy and follow-up.
Antibodies to the yeast Saccharomyces cerevisiae (ie anti-S. cerevisiae antibodies (ASCA))
are more common in Crohn's disease than in ulcerative colitis. Perinuclear antineutrophil
cytoplasmic antibody (p-ANCA), is more common in ulcerative colitis than in Crohn's
disease. These two tests are sometimes useful in differentiating the two conditions but they
are not particularly specific and need to be combined with clinical assessment.
Microbiological testing for infectious diarrhoea including Clostridium difficile toxin is
recommended. In a patient with evidence of Crohn's disease, further investigations are
recommended to examine the location and extent of disease in the small bowel, usually
including small bowel follow-through or small bowel enema and, less often, abdominal
ultrasound, CT and MRI scanning.
Radionucleotide scanning may be used for patients too ill to undergo colonoscopy or barium
studies.
Gastroduodenoscopy and biopsy
