Myositis

Abstract

Cancer patients treated with immune checkpoint inhibitors (ICIs) are known to be at risk for developing immune-related adverse events (irAEs). Myositis, which is characterized by muscle weakness, elevated serum muscle enzyme levels, and inflammatory muscle biopsies, occurs in approximately 0.5% of those treated with ICIs. Those treated with multiple ICIs are at an especially increased risk of developing myositis. Unlike spontaneously occurring myositis patients, those with ICI-induced disease may have ptosis and oculomotor muscle weakness, instead of or in addition to a proximal pattern of muscle weakness. Muscle biopsies from these patients reveal abundant CD4+ and CD8+ T cells. Importantly, as many as 25% of these patients may have co-existing myasthenia gravis and/or myocarditis. Although optimal treatment strategies remain to be defined, corticosteroids with or without other immunomodulating therapies are often effective.