Ulcerative Colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease characterised by diffuse, continuous mucosal and submucosal inflammation of the colon and rectum. Unlike Crohn disease, UC always involves the rectum and extends proximally in a continuous pattern without skip lesions; if inflammation is patchy or rectal-sparing, Crohn colitis should be considered instead. The pathogenesis of UC shares features with Crohn disease, involving a dysregulated immune response to commensal gut bacteria in genetically predisposed individuals, with a family history of inflammatory bowel disease increasing risk by 10-15 fold in first-degree relatives. Inflammation in UC is superficial, affecting only the mucosa and submucosa, unlike the transmural inflammation seen in Crohn disease. The inflammatory infiltrate damages the crypts of the colonic mucosa, leading to cryptitis, which is neutrophil invasion of crypts, and crypt abscesses, the accumulation of neutrophils within crypt lumens. Progressive destruction of crypts results in mucosal ulceration, with surviving mucosa forming inflammatory pseudopolyps that project above the denuded surface. This continuous inflammation, always beginning at the rectum and extending proximally, is a key diagnostic feature. Chronic inflammation causes loss of haustral...