Worldwide Incidence, Prevalence of MG Has More Than Doubled Since 1950s

The global prevalence and incidence of myasthenia gravis (MG) have grown significantly in recent years, according to 70 years’ worth of data.¹

The data, published in Neuroepidemiology, come from a systematic review of over 90 studies between 1952 through 2022, which found that both prevalence and incidence rates have more than doubled throughout the study period.

This is the first systematic review to provide a recent look at MG prevalence and incidence. | Image Credit: © zephyr_p - stock.adobe.com

According to the study researchers, this is the first systematic review to provide a recent look at MG prevalence and incidence, with the last review looking at cases from 1950 up until 2007. That study, which compiled data from 55 studies, found an estimated pooled incidence rate of 5.3 per million person-years (95% CI, 4.4-6.1).²

In the studies used in the current review, those from a similar time frame used in the previous analysis—1967-2007—showed an incidence rate of 8.7 cases per million person-years (95% CI, 5.5-11.9; range, 2.3-21.3), which increased to 22.9 cases per million person-years (95% CI, 14.1-31.7; range, 6.3-61.3) in the later time frame—2008 to 2022.¹

Using the same 2 time frames, the mean prevalence rate increased from 97.5 cases per million person-years (95% CI, 59.9-141.9; range, 20-174.2) to 220.1 cases per million person-years (95% CI, 149.3-288.1; range, 78-475).

Taking a closer look at prevalence, the researchers found a higher risk of MG among women, with a female:male ratio of 1.6:1.

“Several observations suggest that biological factors are important in describing differences in MG epidemiology,” described the researchers. “In this regard, sex is also considered a significant biological factor that determines differences in MG epidemiology. MG affects all ages, but it is considered ‘a disease of young women and old men’. Several studies showed that MG typically affects women at younger ages compared to men: the most common onset age is between 20 and 39 years in women and between 50 and 70 years in men.”

In line with these previous findings, data from the current analysis showed that the women with MG were a median age of 50.4 years, experiencing peak of disease between 25 and 39 years, and the men with MG were a median age of 57 years, with a later onset of peak disease.

Overall, the mean prevalence rate of MG was 173.3 cases per million person-years (95% CI, 129.7-215.5), although the prevalence ranged widely across countries, from 20 to 475 cases per million person-years. Similarly, the incidence rates ranged significantly, from 2.3 to 61.3 cases per million person-years, with a median incidence rate of 15.7 (95% CI, 11.5-19.9).

America had both the highest mean prevalence (256.2 cases per million) and incidence (23.7 per million person-years (95% CI: 6.5-40.9; range: 4.7-61.3). North America, in particular, had mean prevalence rates higher than 300 cases per million (range, 142-475), which the researchers say may be attributable to more common use of national databases or to environmental or genetic factors.

“In this regard, a hypothesis could be related to the high presence of Afro-Americans in North America (especially in the USA), since some studies suggested that rates of autoimmune diseases are higher among these people,” commented the researchers. “However, this finding needs to be investigated and more studies are needed to examine any ethnic or racial differences regarding MG.”

Lower prevalence rates were observed in South America (mean 149.8 cases per million person-years; range, 70-367.1), Europe (mean 167.9 cases per million person-years; range, 20-393), and Asia (mean 127.4 cases per million person-years; range: 67-231). Similarly, Asia (mean 16.9 cases per million person-years [95% CI, 4.8-29; range, 4.2-36.6]) and Europe (mean 17.1 cases per million person-years [95% CI, 11.5-22.7; range, 2.3-46]) had lower incidence rates.

References

1. Sciancalepore F, Lombardi N, Valdiserra G, et al. Prevalence, incidence, and mortality of myasthenia gravis and myasthenic syndromes: a systematic review. Neuroepidemiology. Published online October 9, 2024. doi:10.1159/000539577
2. Carr AS, Cardwell CR, McCarron PO, McConville J. A systematic review of population based epidemiological studies in myasthenia gravis. BMJ Neurol. 2010;10:46. doi:10.1186/1471-2377-10-46