US Incidence, Prevalence of Myasthenia Gravis Rising

Megan Brooks

May 02, 2023

There has been an increase in the incidence and prevalence of myasthenia gravis (MG) in the United States, an analysis of new claims data shows.

Investigators speculate the rise of this rare disorder may be due to "increased diagnosis and more awareness of the disease over time, which has been shown in several studies," study investigator Ema Rodrigues, DSc, MPH, with Alexion Pharmaceuticals, Boston, Massachusetts.

Rodrigues presented her research April 24 at the American Academy of Neurology (AAN) 2023 Annual Meeting.

MG is a rare neuromuscular disease characterized by muscle weakness and fatigue caused by the binding of autoantibodies at the neuromuscular junction. It affects the voluntary muscles of the body, especially those that control the eyes, mouth, throat, and limbs.

In Europe, the incidence and prevalence of MG has increased for the past several decades. In the US, increasing prevalence has also been observed, but recent estimates are lacking, making it tough to gauge the true burden of disease, Rodrigues explained. 

To investigate, Rodrigues and colleagues analyzed claims data (commercial, Medicare, and Medicaid) and electronic health records representing over 300 million patients in the US from 2011 to present.

They calculated sex- and age-specific incidence and prevalence of MG for the year 2021 using US Census data.

Prevalent patients were identified as having one or more MG records in 2021 and two or MG records, at least 30 days apart, from 2016 to 2021. This cohort had 78,225 patients.

Incident patients were identified as those with an MG record in 2021 and no previous MG record from 2019 to 2020. This cohort had 4214 patients.

For both the prevalent and incident cohort, the distribution of male and female patients was roughly 50/50, with a slightly higher proportion of females in the incident cohort, Rodrigues reported.

When looking at age groups, there were "very few pediatric patients," she noted, with less than 1% of the patients under the age of 12. The highest proportion of patients were 65 years or older. The mean age was 67 in the prevalent cohort and 68 in the incident cohort.

In 2021, the overall incidence of MG was 3.2 per 100,000 with similar estimates for males and females (3.2 vs. 3.1 per 100,000, respectively).

Total prevalence was estimated to be 37.0 per 100,000 with sex-specific estimates being comparable at 37.3 and 36.7 per 100,000 for males and females, respectively.

The incidence and prevalence of MG increased with age, ranging from 0.3 and 0.4 per 100,000, respectively, in children younger than age 2 years, to 10.2 and 116.8 per 100,000, respectively, in people 65 and older.

These estimates are "significantly higher" than those from a prior US analysis from 2003, Rodrigues told attendees, but they are quite similar to the estimates that were reported in in Sweden in 2020.

A limitation of the analysis is that patients who do not seek care regularly may have not been identified due to inclusion criteria, potentially leading to underestimates. Also, no information was available on the MG subtype (ocular vs generalized).

Underestimated Burden

Reached for comment, Richard J. Nowak, MD, MS, director of the Yale Myasthenia Gravis Clinic, Yale School of Medicine, New Haven, Connecticut, noted that the new report, "albeit limited as a claims-based analysis, presents modern data on incidence and prevalence of MG in the US."

"It suggests that the current estimates of MG in the US are too low and that the true impact/burden of MG is greater. While we are unable to verify the accuracy of the diagnosis, the total MG population is likely to be about 100,000, which is higher than prior estimates."

"This in fact might be driven by greater disease awareness and increased diagnosis along with decreased mortality and longer life expectancy," Nowak told Medscape Medical News.

"Anecdotally, we are most certainly seeing patients with new-onset MG in their 70s, 80s, and even 90s in recent years. The EXPLORE-MG registry published data from a tertiary center on age of onset breakdown showing MG can present at any age," Nowak added. 

Funding for the study was provided by Alexion, AstraZeneca Rare Disease. Rodrigues receives compensation and owns stock as an employee of Alexion, AstraZeneca Rare Diseases. Nowak has no relevant disclosures.

American Academy of Neurology (AAN) 2023 Annual Meeting. Abstract 2994. Presented April 24, 2023.

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