RESUMO
BACKGROUND: The recent literature suggests that the incidence and prevalence of myasthenia gravis (MG) are changing. We performed a population-based study of MG in the province of Trentino (524,826 inhabitants) and compared the results with those collected 20 years ago. METHODS: Multiple sources of information (discharge diagnosis, antibody tests and anticholinesterase drugs) were analyzed. Incidence was calculated from 2005 to 2009. Prevalence was calculated on December 31, 2009. Comparison was made with descriptive statistics for 1981-1990 for the identical region. RESULTS: Incidence and prevalence greatly increased in comparison with 1981-1990 data. The prevalence rate increased from 82.9 (95% confidence interval, CI, 58.4-114.3) in 1990 to 129.6 (95% CI 100.6-164.3) per million population, whereas the average annual incidence increased from 7.4 (95% CI 5-10.4) per million person-years in 1981-1990 to 14.8 (95% CI 10.5-20.3) in 2005-2009. This increase was mainly due to male patients with late-onset MG. CONCLUSIONS: The study confirms the increase in incidence and prevalence of late-onset MG in the same region 20 years apart. So we should consider MG also as a disease of the elderly.