Underreporting of strictures in the Montreal classification

Background: Crohn's disease (CD) is often complicated by a stricturing and/or fistulating phenotype necessitating surgery. Both complications account for the classification of behavior according to the Montreal Classification (MC) in a hierarchic manner which might lead to loss of information about stricture formation in case of concomitant presence of enteral penetration. Methods: The aim of the study was to identify the underreporting of strictures as defined by the MC. A total of 548 consecutive CD patients who consented to participate in a study programme on genetics were included. For each patient, a detailed chart review was performed and disease-specific data were retrospectively collected according to the definitions of the MC and of a validated documentation standard for IBD (IBDIS, Inflammatory Bowel Disease Information System). The behavior of the MC is graduated in B1 non-stricturing non-penetrating, B2 stricturing, and B3 penetrating in a hierarchic manner. As gold standard for rating of the MC the pathohistological and surgical reports of first surgery were used. Perianal fistulas were excluded from this analysis. Results: Data on 318 (58%) patients undergoing surgery (162 females (55%)) with a median age at diagnosis of 25 years (range 7–66 years) and a median time from diagnosis to first intestinal surgery of 29 months (range 0–294) were available. All patients underwent intestinal resections. The most common procedure was ileocoecal resection (n=173; 54%), other locations of resection were the upper gastrointestinal tract (GIT) (n=21; 7%), ileum (n=29; 9%), colon (n=39; 12%), and ileocolon (n=56; 18%). The behaviour was B1 in 17 (5%), B2 in 96 (30%) and B3 in 205 (64%) subjects. However, among patients classified as B3 (penetrating) strictures were described in addition to the penetrating behaviour in 154 (75%) patients whereas penetration without stricture was seen in 51 (25%) patients. Thus, 154 out of 250 (62%) strictures were combined with penetration. Due to the hierarchic manner of the MC the sensitivity to describe a stricture was only 38%, the specificity was 100%, the positive predictive value was 100% and the negative predictive value was 31%. This results in an accuracy of 52% of the MC to reflect the existence of a stricture. Patients with penetration alone had a significantly shorter duration from diagnosis to first surgery (median 10 months; 0–179 months) than patients with both strictures and penetration (31 months; 0–294 months) as well as patients with strictures only (36 months; 0–263 months) (p<0.05). Conclusion: Strictures are often combined with penetration in CD patients undergoing surgery. This leads to underreporting of strictures in the MC and possibly to heterogeneity of the group of patients with B3 with different clinical outcomes.