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221 THE RISK OF DEVELOPING CROHN'S DISEASE AFTER AN APPENDECTOMY: A POPULATION-BASED COHORT STUDY IN SWEDEN AND DENMARK GG Kaplan1, BV Pedersen2, RE Andersson3,4, BE Sands1, J Korzenik1, M Frisch2 BACKGROUND & AIMS: Studies exploring the relationship between appendectomy and the subsequent risk of Crohn's disease (CD) have reported conflicting findings. This relationship is complicated by the interval between surgery and the diagnosis of CD. In response to the varied results, we conducted a nation-wide cohort study in Sweden and Denmark in order to assess the risk of developing CD after an appendectomy.
1Harvard University, Boston, Massachusetts, USA; 2Statens Serum Institut, Copenhagen, Denmark; 3University Hospital, Linköping, Sweden
METHODS: All patients undergoing appendectomy in Swedish (since 1964) and Danish (since 1977) hospitals were followed for subsequent first hospitalizations for CD through 2004. Ratios of observed-to-expected cases of CD (standardized incidence ratios, SIR) with 95% confidence intervals (CI) served as measures of relative risk.
RESULTS: In Sweden and Denmark, 709,353 individuals underwent an appendectomy and 1655 cases of CD were observed during 11.1 million person-years of follow-up. The overall SIR of developing CD following an appendectomy was 1.52 (95% CI: 1.45 - 1.89), but SIRs depended significantly on the time interval since the operation, the age at appendectomy, and the underlying cause of appendectomy. CD risk was particularly high in the first 6 months (SIR = 8.69; 95% CI: 7.68 - 9.84) but gradually diminished thereafter, reaching background CD incidence levels 10 years after appendectomy. Children appendectomized before their 10th birthday experienced no increase in CD risk (SIR = 1.00; 95% CI: 0.80 - 1.25), while appendectomies after that age were consistently associated with increased risk (SIRs 1.44 to 1.69). Patients whose appendix was removed incidentally (SIR = 1.97; 95% CI: 1.82 - 2.14) or because of perforated appendicitis (SIR = 1.89; 95% CI: 1.66 - 2.16) were at higher CD risk than patients with non-perforated appendicitis (SIR = 1.19; 95% CI: 1.11 - 1.28) (p < 0001).
CONCLUSION: Individuals who undergo appendectomy are at increased CD risk in the first decade after the operation. Complex associations with age at appendectomy, the underlying cause of appendectomy, and the time since the operation offer interpretational challenge. Diagnostic problems in patients with incipient CD almost certainly explain the rather extreme SIRs seen shortly after appendectomy. However, a biological explanation seems warranted to account for the sustained excess of CD diagnoses up to 10 years after appendectomy.