Efgartigimod and Steroid Pulse Therapy as an Early Fast-acting Treatment Strategy for Anti-MUSK Myasthenic Crisis.

We present the case of an 83-year-old Japanese woman with anti-muscle-specific kinase (MUSK)-positive myasthenia gravis (MG) who rapidly progressed from ocular symptoms to a myasthenic crisis requiring mechanical ventilation. Immediate intervention with efgartigimod, a neonatal Fc receptor (FcRn) antagonist, combined with steroid pulse therapy, facilitated the prompt extubation and recovery of the patient. Notably, clinical remission was achieved without plasma exchange or intravenous immunoglobulin administration, and the patient was successfully maintained on tacrolimus without the use of oral corticosteroids. This case suggests that efgartigimod may be effective in acute anti-MUSK MG exacerbations, positioning FcRn inhibition as a promising alternative to conventional fast-acting rescue therapies.