Rising Myasthenia Gravis Rates in Older US Men Spark Research, Public Health Concerns

In a new analysis of myasthenia gravis (MG) in the US, age and gender were strongly associated with higher incidence and prevalence. Notably, a striking rise in MG prevalence in older men prompts questions for basic research, therapeutics, and public health.

Incidence and prevalence of MG have been studied globally for several decades, yielding considerable variations across studies, the authors wrote. Previous research into the rare autoimmune disease shows an incidence range of 1.7 to 28 cases per 1 million person-years and a prevalence range of 15 to 329 per million.

“Given the reported increase of incidence and prevalence of MG at other locations globally, there is a need to provide a contemporary estimate of MG in the US,” they said.

The prevalence of myasthenia gravis has risen among older men in the US

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This population-based study is published in Frontiers in Neurology.

This study aimed to estimate the incidence and prevalence of MG during 2021. According to the authors, these metrics were last examined more than 2 decades ago and have never been investigated in a large, geographically representative dataset. To identify persons living with MG, they applied a previously validated algorithm with high sensitivity and specificity to analyze claims data. When diseases have specific International Classification of Diseases (ICD) codes, claims can be used to capture cases hard to characterize in other sources.

The investigators identified MG cases in 2 Truven databases (commercial and Medicare), which during 2017 included approximately 20 million recipients. Because of similar data structures, the cohorts were combined in the analysis. The multistate Medicaid Database contained more than 10 million enrollees.

The algorithm identified MG if a patient had 1 or more inpatient diagnosis or 5 or more outpatient diagnoses and a test code for single-fiber electromyography or Tensilon test within 1 year, or 3 or more prescriptions of pyridostigmine within 1 year.

Annual incidence and annual population-based prevalence were calculated for patients 18 years or older on January 1, 2017. The commercial and Medicare databases included information on US census regions (Midwest, Northeast, South, and West) but race and ethnicity were not reported. Conversely, most Medicaid enrollees had information on race/ethnicity but not geographic location.

Analysis identified an age- and gender-adjusted incidence of 68.5 new cases per 1 million person-years in the commercial/Medicare cohort during 2017 and an adjusted prevalence of 316.4 per million. Similar yet slightly lower numbers were found in the Medicaid-insured population: 49.7 new cases per 1 million person-years and an adjusted prevalence of 203.7 cases per million.

Given these results, the investigators were able to estimate the number of adult cases of MG in 2021 by extrapolating from the stratified estimates to the population size from the 2021 American Community Survey. They calculated approximately 82,715 adults were living with MG that year.

Overall, the commercially/Medicare-insured cohort had higher incidence and prevalence rates of MG compared with Medicaid enrollees. However, claims-identified cases are based on health care utilization. Lower utilization of ongoing medical services among Medicaid recipients may partially explain the lower estimates in this cohort, the authors suggested.

Among the racial/ethnic groups studied, African American individuals had the highest prevalence and Hispanic individuals had the lowest, at 202.1 and 137.82 per million, respectively. Moreover, African American women had the highest incidence and prevalence among all groups, at 58.7 and 221.04 per 1 million person-years, respectively.

Commercial/Medicare data were examined by geographic region. MG prevalence was lowest in the West and highest in the Midwest, with findings ranging from 137.34 to 228.81 per 1 million population.

Although the investigators observed a steady increase of both incidence and prevalence with age, and the well-known female preponderance for MG under the age of 55, they identified a striking increase of MG prevalence in older men. In commercial/Medicare patients aged 45 to 54 years, prevalence in men vs women was 116.93 vs 197.26 per 1 million, respectively; in patients aged 55 to 64 years, 335.07 vs 280.14 per 1 million; and in those 65 years and older, 1333.88 vs 782.27 per million.

“This pattern of older males having higher MG prevalence than all other subgroups has not been reported previously for any autoimmune disease and is also unprecedented when compared with previous MG epidemiology findings,” they investigators stressed.

Research based on administrative data invariably has limitations. In this study, misdiagnosis or misuse of ICD codes may have affected the validity of some estimates. Moreover, the Truven databases only captured data for actively insured patients.

Still, the authors said the study findings provide a much-needed epidemiological update that includes large geographically and socioeconomically diverse populations.

“In comparison with other MG epidemiology studies conducted globally, we position the US at the upper end of MG prevalence,” the authors concluded. “The causes underlying this trend need to be further evaluated.”

References

Ye Y, Murdock DJ, Chen C, Liedtke W, Knox CA. Epidemiology of myasthenia gravis in the United States. Front Neurol. Published online February 16, 2024. doi:10.3389/fneur.2024.1339167