Is perianal Crohn's disease associated with intestinal fistulization?

BACKGROUND: When cases of Crohn's disease (CD) are described as "fistulizing," distinctions are often not drawn between perianal and intestinal fistulization. The question, therefore, remains open as to whether or not there is truly an association between perianal fistulization and intraabdominal intestinal fistulization in CD. AIMS: We have sought to determine the association between perianal and intestinal fistulization by analyzing the cases of CD recorded in databases from six international centers. PATIENTS: Six databases provided information on 5491 cases of CD in the United States, France, Italy, and The Netherlands. Of these cases, 1686 had isolated ileal disease and 1655 had Crohn's colitis. METHODS: An association between perianal disease and internal fistulae was sought by calculating relative risks for the chance of internal fistulae among patients with perianal fistulae relative to those without. Statistical significance was calculated by the Mantel-Haenszel procedure, stratifying on the separate centers. All statistical tests and estimates were implemented using SAS for the PC. RESULTS: Among the 1686 cases with isolated ileal disease, the evidence of an association between perianal disease and internal fistulization was not consistent across centers, with relative risks ranging from 0.8 to 2.2. For patients with Crohn's colitis (n = 1655), the association was much stronger and more consistent, with an estimated common relative risk of 3.4, 95% confidence interval (2.6-4.6, p < 0.0001). CONCLUSIONS: We have found a statistically significant association between perianal CD and intestinal fistulization, much stronger and more consistent in cases of Crohn's colitis than in cases limited to the small bowel.