PHOENIX – The prevalence is higher than what has been seen in other studies, which could represent a true difference in prevalence, or reflect limitations of the database.
Worldwide estimates suggest that myasthenia gravis affects 700,000 people globally, with incidence rates ranging between 6.3 and 29 per 1,000,000 person-years in Europe and a prevalence between 111.7 and 361 per 1,000,000. Data from Australia, Taiwan, and South Korea also show evidence of increased prevalence in recent years.
However, there is little data about the prevalence of myasthenia gravis in the United States, or about differences between racial groups, according to Bhaskar Roy, MBBS, who presented the study at the 2023 annual meeting of the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM). He noted that most studies are outdated, and the most recent study focused on ocular myasthenia gravis.
True incidence or artifact?
The finding is surprising and may be an artifact of the immature nature of the All of Us database, according to Srikanth Muppidi, MD, who asked about the limitation during the Q&A session following the talk. “The incidence of 0.13 is definitely higher than what we would think would be the true incidence of myasthenia gravis from [clinical experience]. It’s possible that our understanding of true incidence is wrong and this is the actual incidence. What I would like them to do, and I think they’re trying to do, is to look at this finding [and compare it with] other more mature databases and other regional databases. One of the current challenges of All of Us is that our patients are basically being recruited from some parts of the country, and the middle of the country has hardly any presence in the database, so it becomes really challenging to understand it,” Dr. Muppidi said in an interview.
However, Dr. Muppidi, who is a clinical professor of neurology at Stanford (Calif.) Medicine, noted that the All of Us database is still growing. When it has recruited more patients with a diverse population, “it [will be a] valuable source for rare diseases to try to understand true incidence of those diseases,” he said.
Understanding the true prevalence
Dr. Roy recognized the geographic limitations of the database. “Some states, particularly Massachusetts, New York, and California, had a lot of patients in the database, where there were no patients from many states,” said Dr. Roy, associate professor of neurology at Yale University, New Haven, Conn.
He said that the group is working with other databases, including UK Biobank. “The goal is to incorporate all of these databases together [to determine the true incidence],” said Dr. Roy.
It’s critical to understand the true prevalence of myasthenia gravis since new therapies are in development and coming to market. “I worry that myasthenia gravis might be considered less common than it truly is, and that will limit growth of the field if the feeling is that there are not that many [myasthenia gravis patients] in the country,” said Dr. Muppidi.
The study included data from 369,297 adult patients, using Systematized Nomenclature of Medicine (SNOMED) and International Classification of Diseases (ICD) codes to identify patients with myasthenia gravis. There were 479 cases of myasthenia gravis, for a prevalence of 0.13 (95% confidence interval [CI], 0.12-0.14). Of myasthenia gravis patients, 65% were female and the mean age was 64 years. The prevalence of myasthenia gravis in White individuals was 0.16 (95% CI, 0.15-0.18), of which 63% were female, and the mean age was 66 years. The prevalence among Black individuals was 0.078 (95% CI, 0.060-0.10), with 77% of the population female and a mean age of 58 years. The prevalence in Hispanics was 0.091 (95% CI, 0.070-0.12), with 80% female and a mean age of 58 years. Among Asians, the prevalence was 0.056 (95% CI, 0.025-0.12) and 57% were female, with a mean age of 58 years.
The researchers also looked at the EXPLORE-MG database drawn from Yale (n = 3,269,000), which showed a much lower overall myasthenia gravis prevalence of 0.019 (95% CI, 0.017-0.020), a female proportion of 46.8%, and a mean age of 56.6 years. Notably, EXPLORE-MG had a lower proportion of women and a younger population than All of Us.
The researchers compared data from All of Us with other databases for other conditions. The prevalence of ALS was the same as in other conditions, while diabetic neuropathy was significantly lower (2.7 versus 28.5-50 among diabetic patients) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) was higher (0.084 versus 0.028).
Dr. Muppidi has been on advisory boards for Alexion, Argenx, UBC, and Immunovant. Dr. Roy has consulted for Alexion, Takeda Pharmaceuticals, and Argenx and owns stock in Cabaletta Bio. He has received research support from Takeda, Abcuro, and Argenx.