title: Thymectomy for non-thymomatous myasthenia gravis: a propensity score matched study.
abstract: BACKGROUND
  The efficacy of thymectomy in patients with non-thymomatous Myasthenia Gravis (MG) is still unclear. Main limitations have been variable outcome definitions, lack of a control group and adjustment for confounding.
  
  
  OBJECTIVE
  To study the efficacy of thymectomy in achieving remission or minimal manifestation (R/MM) status in patients with non-thymomatous MG.
  
  
  METHODS
  Patients with generalized MG and minimum follow-up of 6 months were included. Demographic data and treatments were recorded, as well as the MGFA post-intervention status at the last visit. Propensity scores were used to create a matched cohort of treated and untreated patients. Standard and Bayesian Cox models were used to study treatment effects.
  
  
  RESULTS
  Of 395 patients included, 183(46%) had a thymectomy. Thymectomy patients were younger (p < 0.001), with more females (p < 0.001) and more patients in MGFA classes 4-5 at diagnosis (p = 0.01). A matched cohort of thymectomized patients and controls (n = 98) was created. The hazard ratio (HR) for the matched cohort was 1.9 (CI:1.6-2.3), favoring thymectomy. The predicted R/MM rate was 21% in treated and 6% in controls at 5 years (Absolute difference:15%). A Bayesian Cox model for the matched cohort had an estimated probability of thymectomy efficacy (HR > 1) of 96% using a non-informative prior, and 79% using a skeptical prior.
  
  
  CONCLUSIONS
  When controlling for potential confounders, thymectomized patients had a higher probability of achieving R/MM status through time compared to controls. This study provides class III evidence of the efficacy of thymectomy in non-thymomatous myasthenia gravis.
authors.affiliation: Division of Neurology - Department of Medicine, University of Toronto and University Health Network, Toronto, Canada. c.barnetttapia@utoronto.ca.|Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada. c.barnetttapia@utoronto.ca.
authors.forename: Carolina
authors.initials: C
authors.lastname: Barnett
authors.affiliation: Division of Neurology - Department of Medicine, University of Toronto and University Health Network, Toronto, Canada. hans.katzberg@utoronto.ca.
authors.forename: Hans D
authors.initials: HD
authors.lastname: Katzberg
authors.affiliation: Division of Thoracic Surgery, Department of Surgery, University Health Network, Toronto, Canada. shaf.keshavjee@uhn.ca.
authors.forename: Shaf
authors.initials: S
authors.lastname: Keshavjee
authors.affiliation: Division of Neurology - Department of Medicine, University of Toronto and University Health Network, Toronto, Canada. vera.bril@utoronto.ca.
authors.forename: Vera
authors.initials: V
authors.lastname: Bril
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis* / Q000601:surgery*; D057216:Propensity Score; D012189:Retrospective Studies; D013934:Thymectomy / Q000639:trends; D016896:Treatment Outcome; D055815:Young Adult