Clinical features and treatment status of adult myasthenia gravis in J apan

Objective Myasthenia gravis ( MG ) is classified as early‐onset MG ( EOMG ; age at onset ≤49 years), late‐onset MG ( LOMG ; age at onset ≥50 years) or thymoma‐associated MG ( TAMG ) (E‐L‐T classification). To clarify the characteristics of each group in the E‐L‐T classification in Japan, we carried out multicenter analyses of MG . Methods A total of 640 adult patients from 11 MG centers participated in the study. Age at onset, sex, clinical symptoms, frequency of crisis, thymic pathology, positivity of autoantibodies against acetylcholine receptor ( AC hR) and muscle‐specific receptor tyrosine kinase (Mu SK ), selected treatment, Cushingoid appearance and post‐intervention status were evaluated in each group. Results EOMG , LOMG and TAMG accounted for 44%, 33%, and 23% of the patients, respectively. Females predominated in the EOMG group (77%), whereas there was no sex difference in the LOMG group. The frequency of ocular MG was the highest in the LOMG group ( EOMG 15%, LOMG 38%, TAMG 12%). Bulbar symptoms and crisis were most frequent in the TAMG group. Anti‐ AC hR antibody was always positive in patients with TAMG ( EOMG 70%, LOMG 78%, TAMG 99%), whereas anti‐Mu SK antibody was never positive in TAMG patients, and more frequently detected in EOMG patients than in LOMG patients. Thymectomy was carried out in 51% of EOMG patients, 26% of LOMG patients and 97% of TAMG patients. Immunotherapy was carried out most aggressively in TAMG patients, and least aggressively in LOMG patients. Minimal manifestations or better with prednisolone ≤5 mg were achieved only in one‐third of EOMG and TAMG patients. Conclusion Thymoma‐associated MG required the most aggressive immunotherapy, followed by early‐onset MG .