, 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.
Dr. Rodrigues presented her research at the 2023 annual meeting of the American Academy of Neurology.
Myasthenia gravis 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 myasthenia gravis has increased for the past several decades. In the United States, increasing prevalence has also been observed, but recent estimates are lacking, making it tough to gauge the true burden of disease, Dr. Rodrigues explained.
Claims-based analysis
To investigate, Dr. Rodrigues and colleagues analyzed claims data (commercial, Medicare, and Medicaid) and electronic health records representing over 300 million patients in the United States from 2011 to present.
They calculated sex- and age-specific incidence and prevalence of myasthenia gravis for the year 2021 using U.S. Census data.
Prevalent patients were identified as having one or more myasthenia gravis records in 2021 and two or more myasthenia gravis records, at least 30 days apart, from 2016 to 2021. This cohort had 78,225 patients.
Incident patients were identified as those with a myasthenia gravis record in 2021 and no previous myasthenia gravis record from 2019 to 2020. This cohort had 4,214 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, Dr. 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 myasthenia gravis 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 myasthenia gravis 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 U.S. analysis from 2003, Dr. Rodrigues told attendees, but they are quite similar to the estimates that were reported 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 myasthenia gravis subtype (ocular vs. generalized).