A national epidemiological study of Myasthenia Gravis in Australia

Background and purpose: Existing epidemiological studies of Myasthenia Gravis have generally examined small populations. Few national studies have been conducted, and published incidence and prevalence rates vary widely. We report one of the largest national studies of Myasthenia Gravis, and the first incidence and prevalence rates for Australia. Methods: Prescriptions for Pyridostigmine Bromide in 2009 were utilized from a national prescribing database to estimate incidence and the prevalence of symptomatic and treated disease. Crude rates were age-standardized to the WHO world population. We compared standardized rates to recent national studies from Norway and Taiwan. Results: In 2009, there were 2574 prevalent cases of symptomatic and treated Myasthenia Gravis, corresponding to an annual crude prevalence rate of 117.1 per 1 million residents. There were 545 incident cases, yielding a crude incidence rate of 24.9 per 1 million residents. The crude incidence in women and men was estimated to be 27.9 and 21.9 per 1 million, respectively. Prevalence and incidence rates were higher in women than men between the ages of 15 and 64 years, and were higher in men than women in those older than 65 years. Rates peaked between the ages of 74 and 84 years, declining thereafter. Standardized incidence was higher in Australia than Norway, but similar to Taiwan (P-values = 0.007 and 1.00, respectively). Conclusions: This first Australian epidemiological study of symptomatic Myasthenia Gravis is one of the largest population-based studies ever reported and supports higher incidence rates for Myasthenia Gravis. Myasthenia Gravis disproportionately affected younger females and older males.