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.

Objective: Under the assumption of irreversibility, the Montreal classification provides a unidirectional assessment of the complications and behaviour of Crohn's disease (CD) that does not allow for downstaging. We examined the use of a bidirectional Montreal classification system that can capture disease regression.

Design: From the BioCrohn Registry, an inception cohort of patients with CD for ≤12 months duration was defined and followed up for 5-years. Cumulative probabilities for developing complications were estimated using the Kaplan-Meier method. Potential associations of explanatory variables with disease progression were estimated with Cox regression.

Results: Among 393 incident CD patients (of whom 255 completed the entire follow-up), the 5-year cumulative probability of developing complications was 41.5% (15.6% and 25.9% for stricturing and penetrating complications respectively). Perianal disease (hazard ratio [95% confidence interval]: 8.45 [4.74-15.07]) and surgical resection of the intestine (2.71 [1.50-4.92]) in the very early phase of the disease were associated with a higher risk of developing a penetrating complication within the 5-year follow-up. The use of a bidirectional Montreal classification system which can account for disease regression demonstrated that 90% of patients exhibited inflammatory disease behaviour at 5 years, in contrast to 58%, if the hierarchical, unidirectional Montreal classification system was used.

Conclusion: An additional bidirectional disease behaviour assessment capturing reversed or fully controlled complications may provide a more realistic appraisal of the complexity and unmet needs of patients treated with advanced therapies.