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Chapter 4: Inflammatory bowel disease 171

Incidence ation, joint pain and swelling, rashes such as erythema
5–6 per 100,000 per year. nodosum, and signs of iritis.

Age
Peak incidence 20–50 years. Macroscopy
In early disease there is oedema of the mucosa and sub-
Sex mucosa resulting in a loss of transverse folds. Later in the
M = F course there is a cobblestone effect due to submucosal
oedema and deep fissured ulcers. Bowel wall thickening
and strictures result from oedema and fibrosis. These
Geography
Incidencevariesfromcountrytocountry,mostcommon areas are interspersed by normal areas of bowel.
in the West.
Microscopy
Aetiology
Transmural (full thickness) inflammatory cell infiltrates
1 Familial: There is significant concordance between
are seen. Ulcers extend deep within the bowel wall, fis-
monozygotic twins. Crohn’s disease is more common
suresandfibrousscarsarealsoseen.Non-caesatinggran-
in relatives of patients.
ulomas in the presence of mucosal changes of inflam-
2 Genetic: HLA B27 is more common in patients with
matory bowel disease are characteristic and diagnostic
IBD. A specific susceptibility gene for Crohn’s disease
of Crohn’s disease.
has been found on chromosome 16, IBD1. This en-
codes a protein, NOD2, which regulates macrophage
activation in response to intracellular lipopolysaccha- Complications
ride. Fibrosis and scarring leads to stricture formation and
3 Smoking: Patients with Crohn’s disease are more likely intestinal obstruction. Inflammation of the serosal sur-
to be tobacco smokers. face may cause adhesions and intestinal obstruction.
4 Some suggestion of infective trigger, but no clear evi- Transmural inflammation may lead to fisulae, perfo-
dence. ration and abscess formation. In long-standing disease
there is an increased incidence of carcinoma of the
Pathophysiology bowel.
Crohn’s disease is a chronic relapsing and remitting in-
flammatory disease that can affect any part of the gas-
trointestinal tract. The site most commonly affected is Investigations
the terminal ileum. The disease may affect a small area of Anaemia may be due to chronic disease, iron defi-
the bowel or may be extensive affecting the whole bowel. ciency or vitamin B 12 or folate deficiency. The platelet
Multiple areas may be affected with normal bowel in- count may be raised in active disease.
between termed ‘skip lesions’. Inflammatory markers such as C reactive protein and
ESR may be raised.
Clinical features Asmallbowelcontrastfollowthroughmayrevealdeep
The clinical picture is dependent on the area affected. ulceration and areas of narrowing (sting sign). Stric-
Colonic disease presents with passage of blood and mu- tures are also demonstrated.
cus, terminal ileal disease often presents with diarrhoea, Colonosocopy with biopsy is diagnostic. Capsu-
abdominal pain and weight loss. Abdominal pain is vari- lar endoscopy can be used to visualise the small
able from chronic to acute, and may occur in any part bowel.
of the abdomen. It may mimic other pathologies such Other investigations include a white cell scan to iden-
as intestinal obstruction or acute appendicitis. Specific tify areas of active inflammation and MRI scanning
features to be elucidated include oral or perianal ulcer- for perianal disease.