Myositis, myasthenia gravis, polyneuropathy and myocarditis: A life-threatening tetrad due to pembrolizumab

The immune-related adverse events (irAEs) are reported more frequently as the employment of these therapies is growing. IrAEs are heterogeneous and potentially serious and their diagnosis do need a high suspicion index. Treatment mostly depends on the type and severity of irAEs and the use of immunomodulators is frequent. We report a tetrad of uncommon irAEs affecting an elderly male with metastatic melanoma treated with pembrolizumab. The patient presented a severe proximal muscle weakness accompanied by two episodes of cardiopulmonary arrest (CPA). The clinical presentation along with raised serum muscular and cardiac enzymes, equivocal dosing of acetylcholine receptor (AChR) and positive anti-striated muscle (anti-SM) antibodies, and characteristic electromyographic findings revealed a probable overlap syndrome myositis, myocarditis, myasthenia gravis and polyneuropathy. The patient showed improvement on muscular strength and remission of the neoplastic disease after sequential treatment with high dose of corticosteroid, plasmapheresis, intravenous immunoglobulin (IVIg) and rituximab.