title: Smoking and socio-economic status may affect myasthenia gravis.
abstract: OBJECTIVE
  The influence of environmental factors in myasthenia gravis (MG) is unknown. The aim of this cross-sectional population-based study was to investigate if smoking and socio-economic status (SES) were associated with MG in the Norwegian population.
  
  
  METHODS
  Subjects were 491 MG patients identified in Norway at the time of the study (point prevalence 12.7/100 000). A questionnaire covering smoking habits and markers of SES (education and occupation) was mailed to all patients. Population data were obtained from Statistics Norway.
  
  
  RESULTS
  A total of 375 (76.6%) patients completed the questionnaire (236 women, mean age 59 ± 18 years), of which 193 reported to be early onset MG (EOMG, onset ≤40 years, 155 women). Compared with the general population, current smoking was more prevalent amongst MG patients [risk ratio (RR) 1.5; 95% confidence interval (CI) 1.1-1.9], most of whom had EOMG. Female MG patients had higher education compared with the general population (RR 4.5; 95% CI 3.2-6.2). Male MG patients were similar to the general population regarding both education and occupation, except for a subset of late onset MG who had shorter education (RR 1.9; 95% CI 1.1-3.2) and had worked in crafts and related trades. About half of working age MG patients received disability pension, a finding significantly related to low educational level and a more severe disease course (P < 0.001).
  
  
  CONCLUSIONS
  This is the first report indicating that smoking and SES may affect MG. Further studies investigating their role as potential risk factors are warranted.
authors.affiliation: Department of Neurology, Oslo University Hospital, Oslo, Norway.
authors.forename: A H
authors.initials: AH
authors.lastname: Maniaol
authors.affiliation: Department of Neurology, Oslo University Hospital, Oslo, Norway.
authors.forename: M
authors.initials: M
authors.lastname: Boldingh
authors.affiliation: Unit of Biostatistics and Epidemiology, Oslo University Hospital, Oslo, Norway.
authors.forename: C
authors.initials: C
authors.lastname: Brunborg
authors.affiliation: Department of Neurology, Oslo University Hospital, Oslo, Norway.|Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
authors.forename: H F
authors.initials: HF
authors.lastname: Harbo
authors.affiliation: Department of Neurology, Oslo University Hospital, Oslo, Norway.|Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
authors.forename: C M E
authors.initials: CME
authors.lastname: Tallaksen
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000453:epidemiology* / Q000209:etiology; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology*; D012923:Social Class; D055815:Young Adult