In contrast with Crohn's disease, neither the Rome nor the Vienna Working Parties had addressed subclassification of ulcerative colitis. On reviewing the present literature, a subclassification system for ulcerative colitis incorporating an assessment of disease extent and severity of an individual relapse of disease were felt to be of critical relevance for recommendation by the Working Party. However, unmet needs were clearly apparent in discussion, of which the most acute appeared to be the need for a classification of longitudinal disease progression, or disease behaviour over time—that is, the frequency of disease relapse and course of disease during the natural history.
The Montreal classification of disease extent of ulcerative colitis allows extent to be defined into three subgroups (table 2).
Table 2Montreal classification of extent of ulcerative colitis (UC)
The subclassification was felt to have clear biological relevance in terms of the response of patients to medical therapy (differential response to topical therapy), and also to be validated by the natural history of the disease, with respect to rates of medication usage, hospitalisation, or colectomy. Moreover, the risk of colorectal malignancy was also felt to provide further validation for this subclassification. In addition, numerous studies show association of specific serological and genetic markers with extensive ulcerative colitis, making this subset of particular importance in the study of its pathophysiology.12,13
“The major drawback of the extent based classification system was clearly identified to be instability of disease extent over time, once again underlining the dynamic nature of inflammatory bowel disease”
The major drawback of the extent based classification system was clearly identified to be instability of disease extent over time, once again underlining the dynamic nature of inflammatory bowel disease. Progression of disease extent over time, together with regression, have been well identified and accepted. The actual risk of proximal extension of proctitis over 10 years is estimated to be as great as 41–54%.1
Progression of left sided colitis may be even higher. The contrary observation is also valid—that disease extent may regress over time, with regression rates estimated from a crude rate of 1.6% to an actual rate of 71% after 10 years.1
In light of this, the Montreal classification proposes the maximal extent of involvement as the critical parameter.
The Working Party has suggested the classification of severity of relapse into four disease activity/severity categories (table 3).
Table 3Montreal classification of severity of ulcerative colitis (UC)
The term fulminant colitis is in variable use, and the Working Party felt that the research agenda in ulcerative colitis must address whether this term has prognostic, value or clinical utility, contrasted with severe relapse of ulcerative colitis, or should be abandoned. Further issues for the research agenda in classification of ulcerative colitis have been identified, and these will need to be addressed. The issue of classification of disease behaviour over time has considerable importance with respect to clinical management, and may also have a direct implication with respect to genetic studies. One of the few studies to have addressed this to date are the detailed studies from Copenhagen where patients with ulcerative colitis were classified into those with prolonged remission, those with intermittent symptoms, and those with continuous disease activity.14
Validation of this classification system and introduction into a further classification scheme may well be directly helpful but will require examination of cohorts of patients, identified either retrospectively or prospectively.
“At the present time, evidence to introduce age of onset as a separate subgroup in ulcerative colitis was felt to be unproven”
At the present time, evidence to introduce age of onset as a separate subgroup in ulcerative colitis was felt to be unproven, either with respect to clinical utility or in a basic research agenda. Other issues that clearly require consideration in a research agenda would be the need for separate classification of colonic disease associated with sclerosing cholangitis. Disease behaviour, extent, and malignancy risk in cohorts of patients with concomitant primary sclerosing cholangitis is increasingly well characterised and, although uncommon, the need for these patients to have a separate classification may well become apparent in further studies.