Clinical features
- Extraintestinal Manifestations (EIM):
- Parallel to bowel inflammation (improves with IBD treatment):
- Peripheral arthritis (type 1: pauciarticular; type 2: polyarticular).
- Cutaneous: Erythema nodosum (painful, pretibial red nodules).
- Ocular: Episcleritis.
- Oral: Aphthous stomatitis.
- Independent of bowel inflammation (does not correlate with disease activity):
- Axial arthropathy: Ankylosing spondylitis, sacroiliitis (HLA-B27 associated). c
- Cutaneous: Pyoderma gangrenosum (deep, necrotic, purulent ulcer with violaceous borders; classic in UC).
- Ocular: Anterior uveitis (photophobia, eye pain).
- Hepatobiliary: Primary Sclerosing Cholangitis (PSC) (strongest association with UC; marked by elevated ALP/GGT, bead-like biliary strictures on MRCP).
- CD-specific metabolic complications:
- Calcium oxalate nephrolithiasis: Fat malabsorption in terminal ileum -> Ca²⁺ binds unabsorbed fatty acids -> free oxalate absorbed in colon -> hyperoxaluria.
- Gallstones: Decreased bile salt reabsorption in diseased terminal ileum -> lithogenic bile.
- Macrocytic anemia: Vitamin B12 deficiency from terminal ileum destruction.