Acute transverse myelitis (ATM) has been reported as rare complication of vaccination. Herein, we report 2 cases of ATM after the administration of an mRNA vaccine for coronavirus disease 2019 (COVID-19). The first one is an 81-year-old man who received the BNT162b2 vaccine. He presented with bilateral hand weakness. Spine magnetic resonance imaging (MRI) showed high signal intensity from the C1 to C3 vertebrae. The second is a 23-year-old woman who received the BNT162b2 vaccine and experienced tingling in her legs. Spine MRI showed a high signal intensity lesion at the conus medullaris. These patients were treated with intravenous methylprednisolone and their symptoms improved slightly. Careful follow-up is needed to identify adverse events after the administration of mRNA vaccines for COVID-19.

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Herein, we report the case of a 48-year-old woman with metastatic thymoma who developed fulminant myositis with cardiotoxicity after one cycle of pembrolizumab treatment. She presented with severe muscle weakness and dyspnea, and her laboratory test results revealed increased muscle and cardiac enzyme levels. Despite an urgent initiation of systemic steroids, her muscle weakness and hypercapnia worsened, for which intravenous immunoglobulin G was initiated. However, hypercapnia did not improve, but the patient recovered completely after plasma exchange. Patients with thymic neoplasms could be susceptible to fulminant forms of immune-related adverse effects because they lack normal thymic physiology. Clinicians must not hesitate to consider immunoglobulin G administration and plasma exchange therapy as the next treatment steps for steroid-refractory patients.K E Y W O R D S immune checkpoint inhibitor, myositis, pembrolizumab, plasma exchange, thymoma