In France, there is a higher incidence and prevalence of myasthenia gravis (MG) than in other European countries.
This is supported by a retrospective population-based study that also discovered a correlation between an increased risk of cancer and the incidence of MG, which tended to rise with age.
In their paper “Epidemiology of myasthenia gravis in France: Incidence, prevalence, and comorbidities based on national healthcare insurance claims data,” published in Revue Neurologique, the researchers stated that “incidence and prevalence rates appear to be significantly higher than in the available literature data for other European countries, and suggest that MG should not be considered a rare disease.”
Self-reactive antibodies target proteins involved in nerve-muscle transmission in MG, an autoimmune illness that causes fatigue and muscular weakening.
Variable incidence and prevalence rates for MG 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, individuals that contract an illness within a given time frame—is referred to as the incidence. The overall number of individuals, both new and existing, within a group that have a particular disorder over time is referred to as the prevalence.
A challenge to previous studies
In order to assess the incidence and prevalence of MG in France, a team led by academics at the Université Clermont Auvergne retrospectively examined data from the Échantillon généraliste de bénéficiares (EGB) from January 2008 to December 2018. The EGB has representative population data for France and is connected to the national health insurance programme in France.
189 women and 142 men, totaling 331 new instances of MG, were found over the course of the 11-year analysis. This translated into an annual incidence of 50.3 cases of MG for males, 56.4 cases for women, and 44 cases for each million individuals.
For both men and women, the incidence of MG grew with age. For women, the incidence began to rise around age 40, while for men, it began to rise at age 60.
Moreover, during the course of the investigation, the prevalence of MG tended to rise. Between 2008 and 2016, there were 331 and 586 cases per million individuals, respectively. The prevalence of MG has continuously exceeded 500 cases per million persons for the last five years under analysis.
“Our findings seem to alter the current understanding of Myasthenia Gravis epidemiology, casting doubt on earlier research done in Western nations, particularly in Europe. Specifically, we discovered 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 over 500 per million people during the study period’s final years, while the literature suggests a range of 15 to 320 per million.”
Analyzing presence of comorbidities
Because there have been reports linking the two conditions, researchers also examined the existence of additional ailments, or comorbidities, in particular cancer.
In this analysis, data from 296 patients were used. When comparing the frequency of thymomas and thymectomy—the surgical removal of the thymus gland—among MG patients, they were 5.1% and 4.7%, respectively, higher than that of the 703,261 individuals from the EGB database who acted as controls (0.015% for thymomas and 0.03% for thymectomy).
Two autoimmune conditions that were more common in MG patients than in controls were thyroid diseases and rheumatoid arthritis (8.5% vs. 1.7% for thyroid illness and 1.4% vs. 0.5% for rheumatoid arthritis). Furthermore, MG patients were treated for cancer at a higher rate (22%) than controls (5.2%) during the research, “indicating a clear excess risk for MG patients to develop cancer.”
“Immunosuppressive drug use, which should be avoided for several years after cancer treatment, raises questions about the management of the disease given the increased risk of cancer among MG patients, especially the elderly.” “Results highlight the necessity of cancer screening for individuals with MG, if not at diagnosis, at least in patients whose disease is difficult to control,” the researchers stated in their report.
