Smoking and socio-economic status may affect myasthenia gravis
Correspondence: A. H. Maniaol, Department of Neurology, Oslo University Hospital, Ullevål, Pb. 4950 Nydalen, 0424 Oslo, Norway (tel.: +47 97674106; fax: +47 23016211; e-mail: email@example.com).
Background and purpose
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.
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.
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).
This is the first report indicating that smoking and SES may affect MG. Further studies investigating their role as potential risk factors are warranted.