Overlap of myasthenia gravis, myocarditis, and inflammatory myopathy secondary to immune checkpoint inhibitor (pembrolizumab) on a background of previously undiagnosed thymoma-associated acetylcholine receptor antibody-positive myasthenia gravis

Immune checkpoint inhibitors have been used successfully over the last several years for treatment of many types of advanced cancer. Those agents cause uncontrolled activation of the immune system frequently resulting in immune-related adverse effects and exacerbation of pre-existing autoimmune diseases. In particular, immune checkpoint inhibitors can cause myasthenia which is usually characterized by an acute onset, rapid progression, and frequent development of myasthenic crisis requiring mechanical ventilation. Coexistence of myasthenia with myocarditis and myositis was shown to be an unfavorable prognostic factor. Steroids, intravenous immunoglobulins, and plasmapheresis are used for treatment of immune checkpoint inhibitor- associated myasthenia.