Sequential and Concurrent C5 and Neonatal Fc Receptor Inhibition in Prolonged Myasthenic Crisis due to Advanced Invasive Thymoma‐Associated Myasthenia Gravis: A Case Report and Literature Review

ABSTRACT Thymoma‐associated myasthenia gravis (TAMG) is frequently refractory, particularly when complicated by myasthenic crisis in advanced invasive disease. Complement C5 inhibitors and neonatal Fc receptor (FcRn) inhibitors have expanded the treatment of acetylcholine receptor (AChR) antibody‐positive generalized myasthenia gravis; however, their optimal selection, sequencing, and combined use in refractory TAMG remain undefined. We report a case of a 46‐year‐old man with Masaoka–Koga stage IVa invasive thymoma and pleural dissemination who developed a prolonged ventilator‐dependent myasthenic crisis after debulking surgery. Immunoadsorption plasmapheresis, intravenous immunoglobulin, and ravulizumab produced only transient benefit. Serum complement activity became undetectable after ravulizumab was switched to zilucoplan (a peptide C5 inhibitor chosen because it is not affected by FcRn blockade), yet sustained respiratory stability was not achieved. Only after subcutaneous efgartigimod was added to ongoing zilucoplan did the patient attain sustained daytime ventilator independence, with a parallel decline in anti‐AChR antibody titer and total immunoglobulin G. He was discharged and remained clinically stable, with no worsening during a subsequent mild infection. Reviewing this case together with previously reported patients who received concurrent or sequentially overlapping C5 and FcRn inhibition, we discuss the biological rationale for dual‐pathway targeting, pharmacological considerations relevant to agent selection and sequencing, and infectious‐safety implications. This temporal association does not establish efficacy; however, combined C5 and FcRn inhibition may be considered, on an individualized basis, in selected refractory TAMG cases when single‐pathway therapy is insufficient.