Development of clinical research on myasthenia gravis: Present and prospective view from Japan

Abstract

The clinical scene of myasthenia gravis (MG) is drastically changing. First, the number of patients is increasing. The epidemiological survey carried out in 2018 showed that the prevalence and patient number nearly doubled compared with the 2006 survey. Onset age is shifting toward elderly. Second, treatment strategy is making progress. Until the first decade of the 2000s, thymectomy and high-dose oral steroids were the mainstream to treat generalized MG. However, adverse effects and impaired quality of life due to steroid administration have become a problem. Japan MG Registry Study Group has been investigating this issue since 2009, and proposed early fast-acting treatment accompanied with low-dose prednisolone to secure patients' quality of life. This strategy is gradually being supported by neurologists in Japan. Third, several molecular targeted drugs have been available since 2017. Additionally, clinical trials of many other drugs are in progress. It is time to reconsider the treatment strategy for MG. Meanwhile, the revised Japanese guidelines for MG and Lambert–Eaton myasthenic syndrome was published in 2022. Three review articles that delineate clinical research on MG in Japan appear in this issue. Suzuki et al. summarized the data of over a period of 10 years from the Japan MG Registry Study. Four crosssectional surveys, as well as a longitudinal study, have been carried out in this period. The early fast-acting treatment strategy was derived from this study. This article introduces the data from the fourth largest multicenter survey in 2021, obtaining detailed clinical information from 1710 consecutive MG patients all over Japan. Yoshikawa described the epidemiological survey of MG in Japan, which he carried out in 2018. He also compared the data with previous surveys, and found (i) increasing prevalence; (ii) increasing lateand elderly-onset; (iii) decreasing female dominance; (iv) decreasing infantile-onset (onset age of 0–4 years); and (v) decreasing frequencies of crisis. Clinical features of MG are greatly changing over time. Murai et al. introduced newly published Japanese clinical guidelines for MG/Lambert–Eaton myasthenic syndrome. In these guidelines, diagnostic criteria of MG were revised, and six clinical subtypes were clarified. It was also mentioned that a high-dose oral steroid regimen with escalation and de-escalation schedule is not recommended. Refractory MG was defined, and a treatment algorithm was proposed. The guidelines are expected to serve to bridge the present with the molecular targeted treatment eras. As aforementioned, detailed clinical research on MG has been carried out for >10 years in Japan. Experiencing the recent significant change in the clinical scene of MG, continuing these studies will become more crucial.