[Myositis induced by immune checkpoint inhibitor therapy]

Immune-mediated myositis can be a severe side effect of cancer treatment involving immune checkpoint inhibitors (ICI). As a distinct type of rheumatic immune-related adverse events (irAE), it presents challenges in terms of diagnosis and patient management. The high mortality and the potential for rapid progression necessitates prompt treatment.

This article provides a practice-oriented overview of myositis-induced irAEs, focusing on the diagnostic and treatment management and the prognostic implications.

A selective literature review was conducted, covering current studies, registry data and pharmacovigilance data as well as guidelines for recognizing and treating ICI-associated myositis irAEs.

Myositis-induced irAEs typically manifest within 1 month of initiating ICI therapy. The incidence is between 0.5% and 1%; however, it is significantly higher with ICI combination therapies. In around half of the cases, myositis is the only irAE manifestation. The number of cases of neuromuscular irAE overlap with myocarditis and/or myasthenia rose from 3.7% before to 8.3% after 2017. Around 20% of cases of isolated myositis require ventilation, compared to 50-80% of cases of overlap syndrome, which is associated with a high mortality of 40%.

If a myositis-irAE is suspected, high-dose glucocorticoid therapy should be initiated immediately. The treatment often includes glucocorticoid-sparing medications. For severe cases, abatacept should be considered as a salvage therapy. Early detection and close collaboration between all medical specialty disciplines involved are crucial for the prognosis of patients.