Definition

• An idiopathic inflammatory bowel disease, characterized by inflammation restricted to the large bowel mucosa, which always involves the rectum and extends proximally in a continuous fashion for a variable distance.

Epidemiology

• Uncommon.

• Major incidence between 15 and 25 y.

 Aetiology and pathogenesis

 • thought to be due to an abnormal mucosal immune response to luminal bacteria.

• the genetic link is weaker than for Crohn’s disease (CD).

 • Smoking appears to decrease the risk of UC.

• One unusual, but consistently confirmed, observation is the protective effect of appendectomy on the subsequent development of UC.

 Presentation

• recurrent episodes of bloody diarrhoea, often with urgency and tenesmus.

Macroscopy

 • erythematous mucosa with a friable, eroded surface and haemorrhage.

 • Inflamed mucosa may form polypoid projections (inflammatory polyps).

 • Disease always involves the rectum and extends continuously to involve a variable amount of colon (fig. 1).

Histopathology

 • Biopsies show almost always show evidence of chronic mucosal damage: crypt architectural distortion, Paneth cell metaplasia, and loss of the inflammatory cell gradient in the lamina propria. there is also mucosal inflammation with cryptitis and crypt abscess formation. Inflammation. the changes are usually more marked distally although the rectal changes may be mild if there has been topical treatment.

 • resection specimens show diffuse inflammation limited to the mucosal layer. Inflammatory polyps may be present.

 • extension of inflammation into the submucosa or muscle layers may occur in very severe acute UC, but the inflammation still remains heaviest in the mucosal layer.

 Prognosis

 • Generally good with treatment.

 • Increased risk of colorectal carcinoma, so surveillance colonoscopy is usually recommended several years after diagnosis.

 • extra- GI manifestations include enteropathic arthropathy , primary sclerosing cholangitis , erythema nodosum , pyoderma gangrenosum , uveitis, and AA amyloidosis.

fig1. Ulcerative colitis. this is a colectomy specimen from a patient with ulcerative colitis. the right colon is on the left of the picture (note the appendix), and the left colon and rectum are on the right side of the picture. the inflamed mucosa, which looks red, begins at the rectum and continuously affects the left colon until the transverse colon where there is a sharp transition into normal mucosa . reproduced with permission from Clinical Pathology (Oxford Core texts), Carton, James, Daly, richard, and ramani, Pramila, Oxford University Press (2006), p. 163, figure 8.15.