Autoimmune Overlap of Systemic Lupus Erythematosus and Myasthenia Gravis: A Case Report and Emerging Therapeutic Strategies

Systemic lupus erythematosus (SLE) and myasthenia gravis (MG) are autoimmune disorders that predominantly affect women and may coexist, though their overlap remains rare.Shared mechanisms, including loss of immune tolerance, B-cell hyperactivity, and dysregulated cytokine signaling, are thought to underlie this association.We report the case of a 56-year-old woman diagnosed with seronegative MG after presenting with progressive proximal weakness, ocular involvement, and electrophysiologic evidence of neuromuscular junction dysfunction.She was stabilized on IVIG, pyridostigmine, and azathioprine.Four years later, she developed a malar rash, polyarthralgia, and bilateral upper-extremity numbness; serologic evaluation confirmed SLE and revealed newly detectable acetylcholine receptor binding antibodies, representing her first positive MG serologic marker.Hydroxychloroquine (HCQ) and methotrexate were added to her regimen.Efgartigimod alfa, a neonatal Fc receptor (FcRn) antagonist, was subsequently initiated for persistent MG and produced marked improvement in MG Activities of Daily Living (MG-ADL) scores.Her SLE-related joint symptoms also improved, although SLE-directed therapy had been adjusted during the same period.However, cyclic dosing resulted in consistent symptomatic wear-off in the days preceding each treatment cycle.Transition to nipocalimab, a fixed-schedule anti-FcRn monoclonal antibody providing continuous IgG suppression, is under multidisciplinary consideration.This case highlights the diagnostic and therapeutic complexity of SLE-MG overlap and suggests that FcRn inhibition may offer a mechanistically rational approach to IgG-mediated disease in both conditions, a possibility that warrants further study.