In France, the incidence and prevalence of the disease are higher. myasthenia gravis (MG) than in other European countries.
This is confirmed by a retrospective population-based study that also found a correlation between increased cancer risk and the incidence of MG, which tended to increase with age.
In their article “Epidemiology of myasthenia gravis in France: incidence, prevalence and comorbidities based on national health insurance claims data,” published in Revue Neurologique, the researchers stated that “the incidence and prevalence rates appear to be significantly higher than in the literature data available for other European countries, and suggest that MG should not be considered a rare disease.”
Autoreactive antibodies target proteins involved in nerve-muscle transmission in MG, an autoimmune disease that causes fatigue and muscle weakness.
Varying incidence and prevalence rates of myasthenia gravis have been documented in research conducted in Europe. However, no epidemiological studies have been conducted in France on these parameters. The number of new cases, that is, people who contract a disease within a given period of time, is called incidence. The total number of people, new and existing, within a group who present with a particular disorder over time is called prevalence.
A challenge to previous studies
To assess the incidence and prevalence of MG in France, a team led by academics from the Université Clermont Auvergne retrospectively examined data from the Échantillon généraliste de bénissants (EGB) from January 2008 to December 2018. The EGB has representative population data for France and is connected to the national health insurance program in France.
During the 11-year analysis, 189 women and 142 men, or a total of 331 new cases of MG, were detected. This translates to an annual incidence of 50.3 cases of MG in men, 56.4 cases in women, and 44 cases per million individuals.
In both men and women, the incidence of MG increases with age. In women, the incidence begins to increase around age 40, while in men, it begins to increase from age 60.
In addition, during the survey, the prevalence of MG tended to increase. Between 2008 and 2016, 331 and 586 cases per million individuals were recorded, respectively. The prevalence of MG has continuously exceeded 500 cases per million individuals during the last five years analyzed.
“Our findings appear to change the current situation understanding myasthenia gravis Epidemiology has cast doubt on previous research conducted in Western countries, particularly in Europe. Specifically, we found an incidence of MG of more than 50 per million person-years, which is significantly higher than the highest estimate of 30 per million person-years reported in the literature, the researchers reported. “The prevalence was more than 500 per million persons in the last years of the study period, whereas the literature suggests a range of 15 to 320 per million.”
Analysis of the presence of comorbidities
Because reports have linked the two diseases, researchers have also looked at the existence of additional diseases, or comorbidities, including cancer.
In this analysis, data from 296 patients were used. When comparing the frequency of thymomas and thymectomy (surgical removal of the thymus) in patients with MG, these rates were 5.1% and 4.7% higher, respectively, than those of the 703,261 individuals in the EGB database who served as controls (0.015% for thymomas and 0.03% for thymectomy).
Two autoimmune diseases were more common in MG patients than in controls: thyroid disease and rheumatoid arthritis (8.5% vs. 1.7% for thyroid disease and 1.4% vs. 0.5% for rheumatoid arthritis). Additionally, MG patients were treated for cancer at a higher rate (22%) than controls (5.2%) during the study, “indicating a clear increased risk for MG patients of developing cancer.”
“The use of immunosuppressive drugs, which should be avoided for several years after cancer treatment, raises questions about disease management given the increased risk of cancer in patients with MG, particularly the elderly,” the researchers note in their report. “The findings highlight the need for cancer screening in people with MG, if not at the time of diagnosis, then in patients whose disease is difficult to control.”
