[An autopsy case of nivolumab-induced myasthenia gravis and myositis]

An 84-year-old woman developed blepharoptosis, diplopia, weakness of extremities, and dysphagia with elevation of serum CK levels after treatment with nivolumab against renal cell carcinoma. 3 Hz repetitive stimulation showed waning in the trapezius muscle, leading to the diagnosis of myasthenia gravis. Laboratory examination showed that anti-acetylcholine receptor antibody was negative. We performed IVIg and steroid therapy. However, her symptoms did not improve, and she died of respiratory failure, although serum CK levels ameliorated to the normal range. The results of autopsy showed atrophy of muscle fibers and massive infiltration of inflammatory cells in the endomysium of the iliopsoas muscle and diaphragm, indicating occurrence of myositis. Immunohistochemical analysis showed that CD8-positive T cells mainly infiltrates in the endomysium with a small number of CD4-potive T cells. Here, we report an autopsy case of nivolumab-induced myasthenia gravis and myositis.