免疫関連有害事象としての重症筋無力症

抄録

Neurological and muscular immune–related adverse events (irAE) associated with cancer treatment with immune checkpoint inhibitors (ICI) include diverse clinical subsets. The diseases affect the central nervous system, peripheral nerves, neuromuscular junction, and muscle. One of representative irAE is myasthenia gravis (MG). Recently, clinical features of MG occurred as irAE (irAE–MG) have been elucidated. Authors previously studied cancer patients who had received monotherapy with nivolumab between September 2014 and August 2016. As the control group, 105 patients with idiopathic MG were used. There were 12 MG cases (0.12%) among 9,869 cancer patients who had been treated with nivolumab. These 12 patients included six men and six women with a mean age of 73.5 ± 6.3 years. MG onset occurred in the early phase after nivolumab treatment and rapidly deteriorated. Nivolumab–related MG (nivoMG) included four patients with mild involvement and eight patients with severe involvement. Bulbar symptoms and myasthenic crisis were observed more frequently in nivoMG than idiopathic MG patients. Serum creatine kinase levels were markedly elevated to an average level of 4,799 IU/L. Among the 12 nivoMG patients, four had myositis and three had myocarditis, with one of these patients having both. Immunosuppressive therapy was effective. In addition, there is a tight association between irAE–MG and myositis, termed as “PD–1 myopathy”. There are guidelines for the diagnosis and treatment of irAE–MG. The prompt and correct recognition of MG following treatment with ICI in cancer patients is important.