Montreal Classification for Inflammatory Bowel Disease (IBD)

Ulcerative Colitis classified by Montreal extent (E1-E3)

→ UC E1 (Proctitis): topical therapy first-line (mesalazine suppositories 1 g OD); surveillance colonoscopy not required until disease extent confirmed beyond rectum; consider step-up if inadequate response; UC E2 (Left-sided): oral + topical mesalazine (combined superior to either alone -- ASCEND II trial); if inadequate response: steroids then immunomodulator (azathioprine/6-MP) or biologic (infliximab, adalimumab, vedolizumab); surveillance colonoscopy from 8 years of disease; UC E3 (Extensive): all of the above plus highest cancer surveillance priority (colonoscopy 1-2 yearly from 8 years); thiopurine or biologic therapy early; colectomy discussion for medically refractory disease; anti-TNF (infliximab) or vedolizumab or tofacitinib for moderate-severe; IBD nurse specialist; MDT management.

Crohn's Disease classified by Montreal A, L, and B categories

→ CD L1 (Ileal): high risk of surgical intervention; budesonide 9 mg OD for active ileitis; maintenance: azathioprine 2-2.5 mg/kg/day or 6-MP; anti-TNF (adalimumab/infliximab) if thiopurine failure; CD L2 (Colonic): mesalazine less effective than in UC; same escalation as above; CD L3 (Ileocolonic): combination of the above; CD L4 modifier: specialist GI or upper GI endoscopy for proximal disease; CD B2 (stricturing): imaging-guided dilatation or surgery; CD B3 (penetrating/fistulising): anti-TNF + azathioprine combination (SONIC trial: superior to monotherapy); fistula assessment (MRI pelvis for perianal); surgical referral for complex fistulae; IBD nurse specialist; nutrition support for active disease; smoking cessation essential (doubles relapse risk in CD); regular stool calprotectin monitoring.