Montreal and Paris classification in UC
| Montreal22 | Paris23 | |||
| Extent* | E1 | Ulcerative proctitis | E1 | Ulcerative proctitis |
| E2 | Left-sided UC (distal to splenic flexure) | E2 | Left-sided UC (distal to splenic flexure) | |
| E3 | Extensive (proximal to splenic flexure) | E3 | Extensive (hepatic flexure distally) | |
| E4 | Pancolitis (proximal to hepatic flexure) | |||
| Severity | S0 | Clinical remission | S0 | Never severe† |
| S1 | Mild UC | S1 | Ever severe† | |
| S2 | Moderate UC | |||
| S3 | Severe UC | |||
*Extent defined as maximal macroscopic inflammation.
†Severe defined by Paediatric Ulcerative Colitis Activity Index (PUCAI) ≥65.