title: Postmenopausal estrogen replacement therapy and increased rates of cholecystectomy and appendectomy.
abstract: BACKGROUND
  Several studies have indicated that estrogen may prime inflammatory and nociceptive pathways, leading to symptoms that mimic cholecystitis. We set out to confirm the relation between recent estrogen use and cholecystectomy in postmenopausal women and to test the novel hypothesis that a similar relation exists for appendectomy.
  
  
  METHODS
  We developed a retrospective cohort using prescribing and surgical procedure information from health administrative databases for approximately 800,000 female residents of Ontario who were over 65 years of age between July 1, 1993, and Mar. 31, 1998. We compared the incidence of cholecystectomy and appendectomy among women recently prescribed estrogen replacement therapy, levothyroxine and dihydropyridine calcium-channel antagonists (DCCA) using age-adjusted Cox proportional hazards models. Patients were followed for a mean of 540 (standard deviation [SD] 449) days.
  
  
  RESULTS
  Compared with women taking DCCA, those who had recently begun taking estrogen were significantly more likely to undergo cholecystectomy (age-adjusted risk ratio [aRR] 1.9, 95% confidence interval [CI] 1.6-2.2) and appendectomy (aRR 1.8, 95% CI 1.1-3.0). No significant difference in either outcome measure was found between the levothyroxine users and the DCCA users.
  
  
  CONCLUSIONS
  This study identifies an increased risk of cholecystectomy and appendectomy among postmenopausal women who have recently begun estrogen replacement therapy.
authors.affiliation: Institute for Clinical Evaluative Sciences, Toronto, Ont.
authors.forename: M M
authors.initials: MM
authors.lastname: Mamdani
authors.forename: K
authors.initials: K
authors.lastname: Tu
authors.forename: C
authors.initials: C
authors.lastname: van Walraven
authors.forename: P C
authors.initials: PC
authors.lastname: Austin
authors.forename: C D
authors.initials: CD
authors.lastname: Naylor
mesh_terms: D000368:Aged; D001062:Appendectomy / Q000706:statistics & numerical data*; D002763:Cholecystectomy / Q000706:statistics & numerical data*; D015331:Cohort Studies; D015914:Estrogen Replacement Therapy / Q000009:adverse effects*; D005260:Female; D006801:Humans; D017698:Postmenopause; D012189:Retrospective Studies; D012307:Risk Factors