To Örebro University

Background: Appendicectomy for acute appendicitis, but not for other causes, is inversely associated with immune-mediated diseases such as ulcerative colitis, suggesting appendicitis is a marker of immune characteristics influencing immune-mediated disease risk. This study investigated the association of appendectomy and its underlying diagnosis with multiple sclerosis (MS). Methods: Swedish general population registers and the Swedish MS register provided information on 20 542 cases with MS diagnosed between 1964-2006 and 204 157 controls matched for age, sex, period and region. Appendicectomy prior to MS diagnosis was identified in 673 cases and 6518 controls. Conditional logistic regression, with adjustment for socio-economic index, assessed the association of diagnosis underlying appendicitis with MS risk. Results: A perforated appendix, the best indicator of acute appendicitis in this material, was inversely associated with MS, although not statistically significantly, with an odds ratio (and 95% confidence interval of 0.86 (0.70-1.04). The odds ratios are 1.04 (0.94-1.16) for appendicitis without perforation and 1.14 (0.98-1.33) for appendectomy without appendicitis. Conclusion: Although inconclusive in terms of assessing the hypothesis, these results may help to explain why earlier studies of appendicitis and MS risk have been inconsistent, as there may be variation in association by diagnosis underlying appendicectomy.