irAEとして発症する重症筋無力症の臨床像

Clinical Features of Myasthenia Gravis as an Immune-related Adverse Event

免疫チェックポイント阻害薬に関連した免疫関連有害事象として発症する神経・筋障害は多彩である。特に重要なのが，重症筋無力症（irAE-MG）であり投与早期に発症し，頻度は1％程度である。急速に進行し球症状やクリーゼを伴う重症例が多く，血清クレアチンキナーゼが高値であり筋炎の特徴を併せ持つ。致死的な心筋炎を合併する場合があり，Kv1.4抗体がバイオマーカーとなる。ステロイドなど免疫療法が有効で，早急に開始する必要がある。

Abstract

Neurological and muscular immune-related adverse events (irAEs) associated with cancer treatment using immune checkpoint inhibitors (ICIs) may show a diverse clinical presentation. Myasthenia gravis (MG) represents a serious irAE associated with the aforementioned therapy. Recent studies have discussed the clinical features of MG that occurs as an irAE (irAE-MG). The incidence of irAE-MG is estimated to be 1%. This complication occurs during the early phase of ICI treatment and rapidly worsens, resulting in severe bulbar muscle involvement and myasthenic crisis and significantly elevated serum creatine kinase levels. MG and myositis, which may occur concomitantly as irAEs are often indistinguishable. Myocarditis is occasionally observed in patients with irAE-MG and can cause severe heart failure and lethal arrhythmias, with a fatal outcome. Kv1.4 antibodies serve as biomarkers of severe irAE-MG and myocarditis. Immunotherapy with corticosteroids is effective for management of irAE-MG and should be initiated promptly. Collaboration between consulting neurologists is necessary for safe management of cancer immunotherapy.