How is inflammatory bowel disease (IBD) classified?

Updated: Jul 26, 2019
  • Author: Leyla J Ghazi, MD; Chief Editor: Praveen K Roy, MD, AGAF  more...
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A system to homogenize the classification of IBD on the basis of disease location and behavior was first established in 1998 in Vienna, Austria. [53] Further developments in the field were reviewed, and the Montreal revision of the Vienna classification was proposed (see below), with special attention to predominant parameters of age at diagnosis, location, and behavior of disease. [54]

Montreal classification system

The Montreal revision of the Vienna system is based on the following 3 variables:

  • Age at diagnosis

  • Disease distribution/location

  • Disease behavior

Age at diagnosis (A) has 3 categories, as follows [54] :

  • A1 – ≤ 16 years

  • A2 – 17-40 years

  • A3 – > 40 years

Disease distribution/location (L) has the following 4 categories, 1 of which is a modifier for upper GI involvement [54] :

  • L1 – Ileal

  • L2 – Colonic

  • L3 – Ileocolonic

  • L4 – Isolated upper GI disease; L4 is a modifier that can be added to L1-L3 when there is concomitant upper GI involvement

Disease behavior (B) has 1 interim category (B1) and 2 specified categories, with an additional modifier for perianal diseases (p), as follows [54] :

  • B1 – Nonstricturing, nonpenetrating; B1p: nonstricturing, nonpenetrating with perianal involvement

  • B2 – Stricturing; B2p: stricturing with perianal involvement

  • B3 – Penetrating; B3p: penetrating with perianal involvement

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