Case Report: Dual response to efgartigimod in myasthenia gravis and comorbid autoimmune disorders: a case series.

The coexistence of myasthenia gravis (MG) with other IgG-mediated autoimmune diseases represents a clinically heterogeneous condition, driven by pathogenic autoantibodies. Efgartigimod, a neonatal Fc receptor antagonist, has the ability to clear all IgG subclasses. Here, we report four cases of MG concomitant with IgG-mediated autoimmune diseases, specifically idiopathic inflammatory myopathies (IIM), Isaacs syndrome, autoimmune encephalitis (AE), and IgG4-related disease (IgG4-RD). All of them demonstrated a favorable therapeutic response to efgartigimod, with marked improvement in QMG and MG-ADL scores, along with disease-specific clinical or laboratory manifestations of the overlapping autoimmune conditions. These cases provide preliminary evidence supporting efgartigimod as a promising treatment option for patients with MG complicated by IgG-mediated autoimmune diseases.