Efgartigimod for induction and maintenance therapy in muscle-specific kinase myasthenia gravis

Background: The efficacy of efgartigimod in treating myasthenia gravis (MG) patients with muscle-specific kinase (MuSK) antibodies has not been demonstrated in the clinical trial, existing case reports, or observational studies. Objectives: To evaluate the efficacy and safety of efgartigimod combined with immunotherapies such as tacrolimus or B-cell depleting agents, as maintenance treatment for MuSK-MG patients. Design: This retrospective study included 14 MuSK-MG patients treated with efgartigimod at three tertiary hospitals from 2023 to 2024. Methods: Data on the activities of daily living (ADL) scores, Quantitative Myasthenia Gravis scores, and the time reaching minimal symptom expression (MSE) were collected. The combined use of steroids, immunosuppressants, and rescue therapies, as well as the adverse event incidence, were also recorded. Results: The mean age at first efgartigimod treatment was 55 ± 18 years old with a median follow-up time of 28 weeks. From baseline to week 4, MG-ADL scores decreased significantly from 10.1 ± 4.0 to 2.2 ± 3.1 ( n = 14, p = 0.001). The majority of patients (92.9%) maintains a reduction of at least 2 points for more than 8 weeks. The median time to achieve MSE was 4 weeks, with 71.4% (10/14) of patients reaching MSE by week 12. In patients receiving CD20 B cell depleting therapy or tacrolimus as maintenance, the time-weighted average dosage of prednisone was 16 mg while that in those with prednisone alone was 37 mg. Of all the 14 patients, one developed an upper respiratory tract infection 4 weeks after rituximab (RTX), and one was infected with herpes zoster virus 13 weeks after RTX. Conclusion: A single-cycle efgartigimod as an induction therapy, combined with immunotherapies such as tacrolimus or B cell depleting agents, as maintenance treatment, could benefit MuSK-MG patients.