Retrospective analysis of efgartigimod use in patients with double-seronegative generalized myasthenia gravis: a case series

•Efgartigimod showed efficacy for generalized myasthenia gravis.•Effect of efgartigimod in seronegative generalized myasthenia gravis is unknown.•16 seronegative generalized myasthenia gravis patients treated with efgartigimod.•Myasthenia gravis activities of daily living scores improved from 9.2 to 7.4.•There were no serious adverse events. The effect of treatment with efgartigimod in seronegative myasthenia gravis (MG) remains unclear. This retrospective study aimed to evaluate symptomatic changes and safety of treatment with efgartigimod in patients with generalized MG (gMG) double-seronegative for acetylcholine receptor antibody and muscle-specific kinase antibody. We reviewed the medical records of double-seronegative gMG treated with 10 mg/kg efgartigimod once/week per cycle (4 weeks) from June 2022 to June 2023. A total of 16 patients were included. MG–activities of daily living (ADL) scores improved from 9.2 to 7.4. Mean prednisolone dose was reduced from 5.4 to 4.1 mg/day. The duration before MG–ADL deterioration after the end of a cycle was 6.1 weeks. Five patients had mild adverse events. This retrospective study revealed no significant treatment benefit in the outcomes of patients with double-seronegative gMG treated with efgartigimod.