Table 1.

The Montreal Classification of CD and UC

Crohn’s disease

Age at diagnosis

A1 Below 16 years

A2 Between 17 and 40 years

A3 Above 40 years

Location

L1 Ileal

L2 Colonic

L3 Ileocolonic

L4 Isolated upper disease*

Behavior

B1 Non-stricturing, non-penetrating

B2 Stricturing

B3 Penetrating

p Perianal disease modifier†

Ulcerative colitis

Extent

E1 Ulcerative proctitis: involvement limited to the rectum (that is, proximal extent of inflammation is distal to the rectosigmoid junction)

E2 Left-sided UC (distal UC): involvement limited to a proportion of the colorectum distal to the splenic flexure

E3 Extensive UC (pancolitis): involvement extends proximal to the splenic flexure

Severity

S0 Clinical remission: asymptomatic

S1 Mild UC: passage of 4 or fewer stools/day (with or without blood), absence of any systemic illness, and normal inflammatory markers (ESR)

S2 Moderate UC: passage of more than 4 stools per day but with minimal signs of systemic toxicity

S3 Severe UC: passage of at least 6 bloody stools daily, pulse rate of at least 90 beats per minute, temperature of at least 37.5°C, hemoglobin of less than 10.5 g/100 mL, and ESR of at least 30 mm/hr

CD, Crohn’s disease; UC, ulcerative colitis; ESR, erythrocyte sedimentation rate.

*L4 is a modifier that can be added to L1–L3 when concomitant upper gastrointestinal disease is present; ^†p is added to B1–B3 when concomitant perianal disease is present.