Therapeutic Responses to Efgartigimod for Generalized Myasthenia Gravis in Japan

Efgartigimod, which has been well tolerated and efficacious in individuals with generalized myasthenia gravis (MG), is available in Japan not only for the treatment of anti-acetylcholine receptor-positive (AChR+) but also anti-muscle-specific receptor tyrosine kinase (MuSK+) and seronegative generalized MG. We report details of the use of efgartigimod for generalized MG in clinical practice in Japan.

We included patients with generalized MG in the 2021 survey of Japan Myasthenia Gravis Registry (JAMG-R) study group who received an initial cycle of efgartigimod between May and September 2022. We defined "responders" as patients who achieved a score ≥2 points for MG activities of daily living (MG-ADL) in the first treatment cycle. The MG composite and the Revised scale of the 15-item Myasthenia Gravis-Quality of Life scale (MG-QOL15-r) were also evaluated.

Of 1,343 JAMG-R patients, 36 (2.7%) started efgartigimod (female 68%, age 53 years). Their serologic profiles were as follows: AChR+, n = 19 (53%); MuSK+, n = 6 (17%); and seronegative, n = 11 (31%). Twenty-six patients (72%) had refractory MG. There were 81 cycles of efgartigimod during the 26-week observation in 34 patients (average, 2.4 cycles). The mean interval between cycles was 5.9 weeks. A continuous 4-weekly infusion of efgartigimod was performed in 65 (80%) of 81 cycles. In the first cycle, the MG-ADL score of the 34 patients decreased significantly from 10.5 ± 4.3 to 6.9 ± 5.1 (p = 0.003). Similarly, the mean MG composite and MG-QOL15-r decreased from 18.4 ± 13.6 to 11.8 ± 9.6 (p = 0.004) and from 19.2 ± 6.3 to 14.2 ± 8.3 (p = 0.007), respectively. Twenty-one (62%) patients were responders. Therapeutic responses were observed in the subsequent cycles. The duration of effectiveness of efgartigimod was varied among the responders; 4 responders had only a single effective cycle. Significant improvement was observed in the MuSK+ patients. Prednisolone dose of 7 patients was reduced. Our examination of the patients' postintervention status revealed that 6 patients achieved minimal manifestations. COVID-19 occurred in 5 patients. We failed to detect clinical or laboratory findings associated with responders.

Efgartigimod can be considered for the treatment of patients with generalized MG who do not achieve minimal manifestations, with a broad flexibility of patient selection and treatment schedules.