A study published recently in CNS Neuroscience and Therapeutics found that disease severity in myasthenia gravis (MG) was associated with several patient characteristics, including age when the disease began, sex, body weight, the type of symptoms at onset and the presence of thymoma.
Researchers also found associations with environmental and socioeconomic factors, such as altitude, latitude, sunlight exposure, air pollution, education and household income. These findings may help researchers better understand why MG affects some people more severely than others.
Sign up here to get the latest news, perspectives and information about myasthenia gravis sent directly to your inbox. Registration is free and only takes a minute.
The study included 2,468 adults in a national MG database who were enrolled between February 2017 and December 2021. The median age when MG began was 49 years, and on average patients had been diagnosed just over 12 months when the study began. Researchers assessed severity using two measures: the MG Activities of Daily Living (MG-ADL) scale, which looks at how MG affects everyday activities, and the Quantitative MG (QMG) scale, which measures physical weakness.
Read more about MG prognosis
Overall, the median MG-ADL score was 3.0 and the median QMG score was 6.0. Higher scores indicate greater disease severity. A total of 522 patients (21.2%) had an MG-ADL score of 6 or higher, while 476 (19.3%) had a QMG score of 11 or higher, indicating more severe disease.
Several characteristics were associated with higher severity. Patients whose MG began at age 65 years or older were more likely to have higher scores. Generalized-onset MG, which affects muscles beyond the eyes, was also strongly associated with greater severity. Patients with thymoma and those who were underweight were more likely to have higher MG-ADL scores. Women were also more likely to have higher QMG scores.
Other factors were associated with lower severity scores. Patients who were overweight or obese had lower MG-ADL and QMG scores. Thymectomy was also associated with lower QMG scores. Higher education and higher monthly household income were associated with lower MG-ADL scores.
Environmental factors also showed associations. Those at higher altitudes, lower annual temperatures and longer sunlight duration generally had higher QMG scores. Those with medium sunlight duration had lower QMG scores. The authors noted that vitamin D deficiency has been linked with higher MG-ADL scores, and suggested that medium sunlight exposure may help with vitamin D levels, while higher levels of sunlight exposure “may activate immune pathways that are unfavorable for disease control.”
For patients, these findings do not mean that moving to a different location, changing body weight or increasing income will necessarily improve MG. The study looked at associations rather than causes, so it cannot determine whether these factors directly change disease severity.
The authors said further research is needed to determine whether environmental factors contribute to MG severity and how they might interact with the underlying autoimmune disease.
“Our findings support further investigation into the role of environmental factors in MG pathogenesis, which is important for disease management and public health policy,” they concluded.
