Appendectomy and Future Risk of Microscopic Colitis: Correlation or Causation?

Abstract

We read with interest the article by Maret-Ouda et al1Maret-Ouda J, et al. Clin Gastroenterol Hepatol.Google Scholar investigating the relationship between appendectomy and microscopic colitis (MC) based on a Swedish nationwide cohort. The authors found a modestly increased risk of developing MC following appendectomy. Because their findings are different from another study,2Laing A.W. et al.Inflamm Bowel Dis. 2006; 12: 708-711Crossref PubMed Scopus (15) Google Scholar several questions deserve attention. First, most cases in this study were diagnosed between 50 and 70 years of age. Several studies have concluded that the role of appendectomy in immune-related colitis, such as MC and ulcerative colitis (UC), applies only to patients who had surgery before the age of 20.3Andersson R.E. et al.N Engl J Med. 2001; 344: 808-814Crossref PubMed Scopus (330) Google Scholar Some studies have found that pathologic changes, such as fibrosis, were found in more than half of appendixes of patients undergoing colectomy for immune-related colitis and this increased with age.4Kahn E. et al.Mod Pathol. 1992; 5: 380-383PubMed Google Scholar These observations would explain why the role of appendectomy in immune-related colitis in some studies was limited to younger patients. Therefore, we question whether the results of Maret-Ouda et al1Maret-Ouda J, et al. Clin Gastroenterol Hepatol.Google Scholar could differ if the study population were analyzed after stratification for patients younger and older than 20 years. Second, some studies have found that appendectomy in the absence of an inflamed appendix was not associated with a decreased risk of other immune-related colitis, such as UC, suggesting that appendicitis rather than appendectomy protects against UC.3Andersson R.E. et al.N Engl J Med. 2001; 344: 808-814Crossref PubMed Scopus (330) Google Scholar Other studies suggest that the effect of appendicitis is actually higher than the effect of appendectomy, which could have been diluted by inclusion of patients without appendicitis. It is not known whether these considerations apply to MC. Third, the relationship between appendectomy and MC seems fairly well established. Logically, this evidence could mean either that appendectomy increases the risk of developing MC or that MC increases the risk of appendectomy. This situation also exists in other immune-related colitis, such as UC, but the relationship is different. For example, some studies found that appendectomy protects against UC because the role of the appendix in the gut immune system might be critical in this respect.5Rutgeerts P. et al.Gastroenterology. 1994; 106: 1251-1253Abstract Full Text PDF PubMed Google Scholar However, other studies found that UC prevents appendectomy, based on the observation that the incidence of UC continues to rise in parallel with long-term decline of appendicitis in the world, and that UC may protect against appendicitis by inducing fibrosis of the appendix. Before either of these hypotheses is accepted further effort should be devoted toward establishing the role of the appendix in the immunoregulation of the human colon and to determine whether patients with MC do indeed undergo more appendectomies before their MC diagnosis. The relationship may as well have been caused by an unknown confounding factor, such as gut microbiota, both leading to an increased risk of appendicitis or appendectomy and an increased risk of developing MC. Appendectomy and Future Risk of Microscopic Colitis: A Population-Based Case-Control Study in SwedenClinical Gastroenterology and HepatologyPreviewMicroscopic colitis (MC) is an inflammatory bowel disease and a common cause of chronic diarrhea. Appendectomy has been suggested to have immunomodulating effects in the colon, influencing the risk of gastrointestinal disease. The relationship between appendectomy and MC has only been sparsely studied. Full-Text PDF Open AccessReplyClinical Gastroenterology and HepatologyPreviewWe appreciate the comments by Drs Dai, Jiang, and Huang on our paper “Appendectomy and Future Risk of Microscopic Colitis: A Population-Based Case-Control Study in Sweden.”1 We agree that the different results compared with previous research highlight the need for more studies on the topic, but as stated in our paper, the previous study emphasized by the authors had significantly fewer patients included, which might have influenced their results.2 Full-Text PDF