Health Dictionary
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Crohn's disease classification
Introduction
Overview
Overview
Crohn’s disease is classified using the Montreal classification (2005), which replaced the 1998 Vienna classification and stratifies patients by three axes: age at diagnosis (A), disease location (L), and disease behavior (B), with modifiers for upper gastrointestinal involvement (L4) and perianal disease (p).[1][2] Disease location is relatively stable over time, whereas disease behavior commonly progresses from inflammatory to stricturing or penetrating phenotypes.[3] The Paris classification (2011) adapts the Montreal system for pediatric patients.[4]
Classification
Classification
Crohn’s disease is a transmural inflammatory disease that can involve any segment of the gastrointestinal tract from mouth to anus; rectal sparing is typical but not obligatory.[5] Phenotypic classification is recommended at diagnosis because location, behavior, and age at onset carry prognostic weight.[6]
Montreal Classification
The Montreal classification is the most widely used phenotypic classification of Crohn’s disease in clinical practice and research.[1][2]
| Axis | Category | Code |
|---|---|---|
| Age at diagnosis (A) | ≤16 years | A1 |
| 17–40 years | A2 | |
| >40 years | A3 | |
| Location (L) | Terminal ileum (± limited cecal disease) | L1 |
| Colon | L2 | |
| Ileocolonic | L3 | |
| Upper GI disease (modifier; added to L1–L3 when concomitant) | L4 | |
| Behavior (B) | Non-stricturing, non-penetrating (inflammatory) | B1 |
| Stricturing | B2 | |
| Penetrating | B3 | |
| Perianal modifier | Perianal disease (added to B1–B3 when present) | p |
- Examples: a patient diagnosed at age 23 with ileal stricturing disease and no perianal involvement is A2L1B2; a patient diagnosed at age 21 with ileocolonic disease, an intra-abdominal abscess, and perianal fistulas is A2L3B3p.
Location (L)
- Location is a relatively stable trait; in a 10-year cohort, location changed in approximately 16% of patients.[3]
- Approximate distribution at diagnosis:[5]
- Ileocolonic (L3): ~35–45%
- Ileal (L1): ~30%
- Colonic (L2): ~20%; may be difficult to distinguish from ulcerative colitis
- Isolated upper GI (L4): <5%
- Location correlates with behavior: ileal disease is more often stricturing, whereas colonic and ileocolonic disease are more often penetrating.[3]
Behavior (B)
- B1 (inflammatory): inflammation without stricture or penetrating complications.
- B2 (stricturing): constant luminal narrowing with prestenotic dilation and/or obstructive signs or symptoms, without penetrating disease.
- B3 (penetrating): intra-abdominal fistula, inflammatory mass, and/or abscess not attributable to a postoperative complication; isolated perianal or rectovaginal fistulas do not qualify as B3.[2]
- A key change from the Vienna classification was removal of perianal fistulizing disease from the penetrating category and its recording as a separate modifier (p), because perianal disease can coexist with any behavior category.[2][7]
Behavior Migration
- Unlike location, behavior is dynamic and progresses through repeated cycles of inflammation and tissue repair.[8]
- In a 10-year cohort, approximately 46% of patients changed behavior category, predominantly from B1 to B2 or B3.[3]
- In a large referral-center cohort, the cumulative probability of stricturing or penetrating disease reached approximately 88% at 20 years.[9]
- In the prospective BioCrohn inception cohort (advanced-therapy era), the 5-year cumulative probability of complications was 41.5% (stricturing 15.6%, penetrating 25.9%).[10]
- In the Swiss IBD Cohort Study, immunosuppressive therapy and anti-TNF therapy for more than 1 year were associated with a lower risk of migration from B1 to complicated behavior.[11]
Paris Classification (Pediatric)
The Paris classification modifies the Montreal system for pediatric-onset Crohn’s disease while preserving compatibility with adult classification:[4]
| Axis | Paris modification |
|---|---|
| Age (A) | A1a: 0 to <10 years; A1b: 10 to <17 years; A2: 17–40 years; A3: >40 years |
| Location (L) | L4a: upper disease proximal to the ligament of Treitz; L4b: upper disease distal to the ligament of Treitz and proximal to the distal third of the ileum |
| Behavior (B) | Adds B2B3 for stricturing and penetrating disease in the same patient, either simultaneously or at different times |
| Growth (G) | G0: no evidence of growth delay; G1: growth failure |
Diagnostic Requirements for Accurate Classification
- Complete phenotyping requires ileocolonoscopy with ileal intubation and biopsies plus cross-sectional small-bowel imaging (e.g., MR enterography or CT enterography) to define location and detect stricturing or penetrating complications.[6]
- Behavior should be reassessed over time; new obstructive symptoms, abscess, or fistula indicate migration to B2 or B3.[8]
References
References
- ↑ 1.0 1.1 Silverberg MS, Satsangi J, Ahmad T, Arnott ID, Bernstein CN, Brant SR; et al. (2005). “Toward an integrated clinical, molecular and serological classification of inflammatory bowel disease: report of a Working Party of the 2005 Montreal World Congress of Gastroenterology”. Can J Gastroenterol. 19 (Suppl A): 5A–36A. doi:10.1155/2005/269076. PMID 16151544.
- ↑ 2.0 2.1 2.2 2.3 Satsangi J, Silverberg MS, Vermeire S, Colombel JF (2006). “The Montreal classification of inflammatory bowel disease: controversies, consensus, and implications”. Gut. 55 (6): 749–53. doi:10.1136/gut.2005.082909. PMID 16698746.
- ↑ 3.0 3.1 3.2 3.3 Louis E, Collard A, Oger AF, Degroote E, Aboul Nasr El Yafi FA, Belaiche J (2001). “Behaviour of Crohn’s disease according to the Vienna classification: changing pattern over the course of the disease”. Gut. 49 (6): 777–82. doi:10.1136/gut.49.6.777. PMID 11709511.
- ↑ 4.0 4.1 Levine A, Griffiths A, Markowitz J, Wilson DC, Turner D, Russell RK; et al. (2011). “Pediatric modification of the Montreal classification for inflammatory bowel disease: the Paris classification”. Inflamm Bowel Dis. 17 (6): 1314–21. doi:10.1002/ibd.21493. PMID 21560194.
- ↑ 5.0 5.1 Torres J, Mehandru S, Colombel JF, Peyrin-Biroulet L (2017). “Crohn’s disease”. Lancet. 389 (10080): 1741–55. doi:10.1016/S0140-6736(16)31711-1. PMID 27914655.
- ↑ 6.0 6.1 Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE (2018). “ACG Clinical Guideline: Management of Crohn’s Disease in Adults”. Am J Gastroenterol. 113 (4): 481–517. doi:10.1038/ajg.2018.27. PMID 29610508.
- ↑ Gasche C, Scholmerich J, Brynskov J, D’Haens G, Hanauer SB, Irvine EJ, Jewell DP, Rachmilewitz D, Sachar DB, Sandborn WJ, Sutherland LR (2000). “A simple classification of Crohn’s disease: report of the Working Party for the World Congresses of Gastroenterology, Vienna 1998”. Inflamm Bowel Dis. 6 (1): 8–15. PMID 10701144.
- ↑ 8.0 8.1 Roda G, Chien Ng S, Kotze PG, Argollo M, Panaccione R, Spinelli A, Kaser A, Peyrin-Biroulet L, Danese S (2020). “Crohn’s disease”. Nat Rev Dis Primers. 6 (1): 22. doi:10.1038/s41572-020-0156-2. PMID 32242028 Check
|pmid=value (help). - ↑ Cosnes J, Cattan S, Blain A, Beaugerie L, Carbonnel F, Parc R, Gendre JP (2002). “Long-term evolution of disease behavior of Crohn’s disease”. Inflamm Bowel Dis. 8 (4): 244–50. doi:10.1097/00054725-200207000-00002. PMID 12131607.
- ↑ Bokemeyer B, Plachta-Danielzik S, di Giuseppe R, Helwig U, Teich N, Schmidt C, Hartmann P, Sobotzki C, Schreiber S (2023). “Evaluation of a downstaging, bidirectional version of the Montreal classification of Crohn’s disease: analysis of 5-year follow-up data from the prospective BioCrohn study”. Aliment Pharmacol Ther. PMID 37051808 Check
|pmid=value (help). - ↑ Cernoch PS, Fournier N, Zeitz J, Scharl M, Morell B, Greuter T, Schreiner P, Misselwitz B, Safroneeva E, Schoepfer AM, Vavricka SR, Rogler G, Biedermann L (2020). “Lower Risk of B1-to-pB3-Stage Migration in Crohn’s Disease upon Immunosuppressive and Anti-TNF Treatment in the Swiss IBD Cohort Study”. Dig Dis Sci. 65 (9): 2654–63. doi:10.1007/s10620-019-05978-9. PMID 31797187.
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Fahad Hasan, M.D.[2] Aditya Ganti M.B.B.S. [3]