At the 2005 Montreal World Congress of Gatroenterology a classification for Crohn's Disease (CD) was proposed to describe clinical features that are impact the disease course. This is an extension of the Vienna classification (see above). It should be viewed as a dynamic model that can change as the disease evolves.
Parameters:
(1) age at diagnosis (A)
(2) location (L) based on maximal extent of the disease prior to the first bowel resection
(3) behavior (B)
Parameter
Finding
Designation
age at diagnosis
< 16 years
A1
16 to 40 years
A2
> 40 years
A3
location
terminal ileum with or without involvement of the cecum
L1
colon
L2
both ileum and colon
L3
upper GI tract
L4
behavior
non-stricturing, non-penetrating
B1
stricturing (without penetrating features)
B2
penetrating
B3
perianal disease
p
where:
• Penetrating disease involves intra-abdominal or perianal fistula, perianal ulcer, inflammatory mass, or abscess, with or without strictures.
Differences from the Vienna classification:
(1) Age < 40 years is subdivided into 2 groups.
(2) Upper GI tract involvement (L4) can be combined with other location indicators.
(3) "p" for perianal is a modifier that can be added to B1 to B3.
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