Crohn Disease and Ulcerative Colitis

Inflammatory bowel disease (IBD) is driven by a dysregulated immune response that produces chronic gastrointestinal inflammation. Crohn disease and ulcerative colitis share this inflammatory basis, but the location and depth of inflammation create very different clinical patterns. Crohn disease can affect any gastrointestinal segment, from mouth to anus, and can extend through the full bowel wall. Patchy “skip” areas are typical. Full-thickness inflammation explains why Crohn disease causes strictures, obstruction, fistulas, and abscesses: inflammation can scar the lumen, tunnel through the bowel wall, or form a walled-off infection. Ulcerative colitis is limited to the colon and its mucosa. It begins in the rectum and extends proximally in a continuous pattern. Because the inflamed mucosa bleeds and loses its ability to absorb and contain stool normally, urgency, frequent stools, mucus, and visible blood are common. Severe colitis can progress to toxic megacolon, in which colonic dilation greater than 6 cm occurs with systemic toxicity. A client with chronic diarrhoea, weight loss, and a draining perianal opening has a pattern that points toward transmural Crohn disease. A client with repeated urgent, bloody...