title: The risk of developing Crohn's disease after an appendectomy: a population-based cohort study in Sweden and Denmark.
abstract: BACKGROUND
  The relationship between appendectomy and Crohn's disease is controversial. A Swedish-Danish cohort study was conducted to assess the risk of developing Crohn's disease after an appendectomy.
  
  
  METHODS
  709 353 appendectomy patients in Sweden (since 1964) and Denmark (since 1977) were followed for first hospitalisations for Crohn's disease to 2004. Standardised incidence ratios (SIR) served as relative risks.
  
  
  RESULTS
  Overall, 1655 Crohn's disease cases were observed during 11.1 million person-years of follow-up. Whereas appendectomy before the age of 10 years was not associated with the risk of Crohn's disease (SIR 1.00; 95% CI 0.80-1.25), the overall SIR of developing Crohn's disease was 1.52 (95% CI 1.45-1.59), being highest in the first 6 months (SIR 8.69; 95% CI 7.68-9.84). SIR diminished rapidly thereafter, with the risk of Crohn's disease reaching background levels after 5-10 years for Crohn's disease overall, as well as for Crohn's ileitis, ileocolonic Crohn's disease, Crohn's colitis and other/unspecified Crohn's disease. A long-term increased risk of Crohn's disease up to 20 years after the appendectomy was seen only in appendectomy patients without appendicitis or mesenteric lymphadenitis.
  
  
  CONCLUSIONS
  The transient increased risk of Crohn's disease after an appendectomy is probably explained by diagnostic bias.
authors.affiliation: MGH Crohn's and Colitis Center, Boston, Massachusetts, USA.
authors.forename: Gilaad G
authors.initials: GG
authors.lastname: Kaplan
authors.forename: Bo V
authors.initials: BV
authors.lastname: Pedersen
authors.forename: Roland E
authors.initials: RE
authors.lastname: Andersson
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Sands
authors.forename: Joshua
authors.initials: J
authors.lastname: Korzenik
authors.forename: Morten
authors.initials: M
authors.lastname: Frisch
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001062:Appendectomy / Q000009:adverse effects* / Q000706:statistics & numerical data; D001064:Appendicitis / Q000601:surgery; D002648:Child; D003424:Crohn Disease / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008640:Mesenteric Lymphadenitis / Q000601:surgery; D008875:Middle Aged; D011184:Postoperative Period; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology