title: Endometriosis and systemic lupus erythematosus: a population-based case-control study.
abstract: OBJECTIVE
  To investigate the association between endometriosis and systemic lupus erythematosus (SLE) in prospectively collected population-based data.
  
  
  METHODS
  We conducted a case-control study using Swedish registers, identifying female SLE cases from the National Patient Register and female controls sampled from the general population matched on birth year, sex and county during 1964-2011. We identified endometriosis diagnoses from the National Patient Register using ICD codes. We estimated odds ratios and 95% confidence intervals using conditional logistic regression models.
  
  
  RESULTS
  We identified 2834 cases of SLE and 14,164 controls. Seventy-eight cases were diagnosed with endometriosis prior to their SLE diagnosis and 288 controls were diagnosed prior to the index date. We observed a significant association between endometriosis and subsequent SLE with an odds ratio of 1.39 (95% confidence interval = 1.09-1.78). The association was similar when requiring a laparoscopy/laparotomy within six months of the endometriosis diagnosis (odds ratio = 1.33; 95% confidence interval = 0.84-2.12) while the association was stronger when restricted to endometriosis diagnosed at the same time as hysterectomy (odds ratio = 2.26; 95% confidence interval = 1.47-3.64).
  
  
  CONCLUSIONS
  Our findings suggest an association between endometriosis and SLE. Future prospective studies with extended follow-up will be necessary to clarify whether this association is influenced by the timing and severity of endometriosis diagnosis.
authors: Division of Nutritional Epidemiology, The National Institute for Environmental Medicine, Karolinska Institute, Stockholm, Sweden Obstetrics and Gynecology Epidemiology Center, Brigham and Women's Hospital, Boston, Massachusetts, USA holly.harris@ki.se.
authors: H R
authors: HR
authors: Harris
authors: Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institute, Stockholm, Sweden Division of Epidemiology, Department of Health Research and Policy, Stanford School of Medicine, Stanford, USA Division of Immunology & Rheumatology, Department of Medicine, Stanford School of Medicine, Stanford, USA.
authors: J F
authors: JF
authors: Simard
authors: Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institute, Stockholm, Sweden.
authors: E V
authors: EV
authors: Arkema
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D016208:Databases, Factual; D004715:Endometriosis / Q000453:epidemiology*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008180:Lupus Erythematosus, Systemic / Q000453:epidemiology*; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology
keywords: Endometriosis; epidemiology; systemic lupus erythematosus