Ulcerative colitis hub
How Far Does UC Go? (Montreal E1–E3)
Last Updated Nov 11, 2025
Ulcerative colitis (UC) always starts in the rectum and can extend upward in a continuous line. The Montreal system labels the farthest reach at diagnosis: E1, E2, or E3. These labels help choose between topical medicines placed in the rectum and systemic medicines taken by mouth or injection. Extent also guides cancer surveillance and follow up over time. (academic.oup.com)
Key takeaways
E1 means rectum only, E2 means up to the splenic flexure, E3 means beyond the splenic flexure. (academic.oup.com)
For mild to moderate E1 or E2, rectal mesalamine works best at the inflamed site, often combined with oral mesalamine for E2. (gastro.org)
Suppositories treat the rectum, foams spread to rectum and sigmoid, enemas often reach the splenic flexure. (pubmed.ncbi.nlm.nih.gov)
E3 usually needs systemic therapy; rectal medicines can be added for lingering rectal symptoms. (gastro.org)
Disease extent can enlarge over time, about one in four people with limited UC extend within 10 years. (pubmed.ncbi.nlm.nih.gov)
Cancer surveillance depends on extent. Proctitis alone usually does not need IBD‑specific colonoscopy surveillance. Left‑sided colitis and pancolitis do. (crohnscolitisfoundation.org)
What E1, E2, and E3 mean
E1, ulcerative proctitis: inflammation limited to the rectum.
E2, left‑sided colitis: extends from the rectum up to, but not beyond, the splenic flexure.
E3, extensive colitis or pancolitis: extends proximal to the splenic flexure.
These labels reflect the farthest continuous extent seen on endoscopy with biopsies. Extent and clinical severity are recorded separately, and both guide treatment. (academic.oup.com)
Why extent matters for treatment
Topical therapy delivers drug right to the inflamed lining. Systemic therapy treats the whole colon and immune system. Matching the medicine to how far disease goes improves remission rates and limits side effects. Guideline groups recommend rectal mesalamine for distal disease, adding oral mesalamine for left‑sided disease, and using systemic therapies when disease is extensive or more active. (gastro.org)
Choosing topical versus systemic therapy by extent
Extent (Montreal) | Where inflammation is | First‑line for mild–moderate disease | Best rectal option | When to add systemic therapy | Notes |
|---|---|---|---|---|---|
E1, proctitis | Rectum | Rectal mesalamine 1 g daily for induction, then 1 g daily for maintenance | Suppository | If not responding to optimized rectal 5‑ASA, consider rectal steroid, add oral 5‑ASA, or use oral steroids; escalate if symptoms are moderate–severe | High remission with suppositories, good retention. (journals.lww.com) |
E2, left‑sided | Rectum to splenic flexure | Oral mesalamine 2–3 g daily plus rectal mesalamine | Enema for reach, foam if enema not tolerated | If inadequate response, consider high‑dose oral mesalamine plus rectal, then budesonide MMX or short oral steroid course; escalate if moderate–severe | Combining oral and rectal works better than oral alone. (gastro.org) |
E3, extensive/pancolitis | Beyond splenic flexure | Systemic therapy guided by activity and risk; oral mesalamine may help in mild cases | Rectal therapy can be added for rectal bleeding or urgency | Moderate–severe disease usually needs advanced therapy per AGA/ACG living and updated guidelines | Choose by efficacy, safety, and prior exposure. (gastro.org) |
How far do rectal treatments reach
Suppositories coat only the rectum, ideal for E1. Scintigraphy studies show spread confined to the rectum. (pubmed.ncbi.nlm.nih.gov)
Foam enemas typically spread to the rectum and sigmoid, sometimes to the descending colon, with even coating and good retention. (pubmed.ncbi.nlm.nih.gov)
Liquid enemas often reach the splenic flexure, covering most left‑sided disease. Many patients show spread to the splenic flexure within 2 hours. (pubmed.ncbi.nlm.nih.gov)
These reach patterns explain why suppositories suit E1, foams suit proctosigmoiditis, and enemas suit E2. (pubmed.ncbi.nlm.nih.gov)
Practical induction and maintenance tips
E1 proctitis: start with mesalamine suppository 1 g nightly for 2 to 8 weeks. For maintenance, 1 g daily or a few times per week lowers relapse risk. If symptoms persist, add oral mesalamine or a rectal steroid. (journals.lww.com)
E2 left‑sided: combine oral mesalamine with a nightly mesalamine enema. This speeds bleeding control and improves mucosal healing more than oral therapy alone. If response is suboptimal, increase oral dose and continue rectal therapy before moving to steroids. (gastro.org)
E3 extensive: select systemic therapy based on disease activity and prognosis. For moderate to severe activity, guidelines recommend advanced therapies such as anti‑TNF agents, anti‑integrin, JAK inhibitors, S1P modulators, and IL‑12/23 or IL‑23 inhibitors. Rectal therapy may still help with urgency and bleeding. (gastro.org)
Extent can change, so reassess
About one quarter of people with limited UC extend over time, most within 10 years. Younger age at diagnosis carries higher risk of extension. New or worsening symptoms, rising fecal calprotectin, or anemia should prompt reassessment and, when needed, repeat endoscopy to confirm extent. Treatment plans should be updated if disease spreads. (pubmed.ncbi.nlm.nih.gov)
Cancer prevention and surveillance
Cancer risk rises with how much colon is inflamed and how long it has been inflamed. People with at least left‑sided UC usually begin dysplasia surveillance about 8 to 10 years after symptom onset, with colonoscopy every 1 to 3 years based on risk factors and inflammation control. Those with disease limited to the rectum generally do not require IBD‑specific surveillance beyond average‑risk screening. (pubmed.ncbi.nlm.nih.gov)
FAQs
Can rectal therapy help if the disease is extensive
Yes, rectal mesalamine or steroid foam can be added to systemic therapy to control rectal bleeding and urgency. It treats the most inflamed distal segment while systemic therapy treats the rest of the colon. (gastro.org)
Which is better, foam or liquid enemas
Both work. Foams spread evenly and are easy to retain, often covering rectum and sigmoid. Liquid enemas reach higher, often to the splenic flexure, which is helpful for left‑sided disease. Choice depends on disease reach and comfort. (pubmed.ncbi.nlm.nih.gov)
If proctitis is mild, is oral medicine needed
Often no. Suppositories alone are effective for E1. If symptoms persist or recur, adding oral mesalamine improves control. (journals.lww.com)
When should therapy move from mesalamine to advanced treatments
If optimized oral plus rectal mesalamine and short steroid courses do not achieve remission, or if disease is moderate to severe, guideline groups recommend moving to advanced therapies rather than repeating steroids. (gastro.org)