Definition

 • An idiopathic inflammatory bowel disease, characterized by multifocal areas of inflammation which may involve any part of the GI tract.

 Epidemiology

 • Uncommon.

 • Major incidence between 20 and 30 y.

 Aetiology and pathogenesis

 • thought to be caused by an abnormal mucosal immune response to luminal bacteria in genetically susceptible individuals.

 • NOD2 (nucleotide oligomerization binding domain 2) mutations are relatively common, although only 10% of individuals with risk- associated variants develop the disease.

 • Smoking increases the risk.

• A true infectious aetiology remains unproven, although mycobacteria have been long suspected to play a role.

 Presentation

 • Crampy right iliac fossa pain and diarrhoea, which is usually not bloody.

• fever, malaise, and weight loss are common.

Macroscopy

 • Disease usually involves the terminal ileum and colon.

• Affected bowel is thickened with encroachment of mesenteric fat around the anti- mesenteric border of the bowel (‘fat wrapping’).

• Adhesions and fistulae may be seen between adjacent loops of bowel.

• the mucosal surface shows linear ulceration and ‘cobblestoning’.

Histopathology

 • Mucosal biopsies: variability of inflammation within a single biopsy and between several biopsies is the key feature. this is typically manifested by discrete areas of inflammation adjacent to histologically normal crypts. Surface erosions and ulceration may be present. Poorly formed granulomas may be seen, but these are generally uncommon.

 • there may be evidence of chronicity with architectural changes, Paneth cell metaplasia, and loss of the inflammatory cell gradient. If not, the differential diagnosis of focal acute inflammation includes an infectious colitis.

 • resection specimens: deep fissuring ulcers separated by relatively normal mucosa. Lymphoid aggregates are present in the submucosa and muscular layers. Poorly formed granulomas may be seen. these need to be distinguished from a giant cell reaction associated with a ruptured crypt. transmural inflammation is the key diagnostic feature, although it may be seen in the toxic megacolon associated with ulcerative colitis (UC).

Prognosis

 • relapsing and remitting course.

• Most patients require surgery at some point to relieve symptoms from obstruction or fistula formation.

 • Increased risk of small and large bowel adenocarcinomas.

 • extra- GI manifestations include enteropathic arthropathy , anterior uveitis, gallstones, primary sclerosing cholangitis, erythema nodosum , and Pyoderma gangrenosum.