Arthritis and Myositis in a Patient Treated with Programmed Cell Death-1 (PD-1) Inhibitor Pembrolizumab for Lung Cancer

Immune checkpoint inhibitors (ICIs) are a new class of drug that have demonstrated efficacy across many cancer types. Because of their nature and mode of action, ICIs unleash immune activation raising concerns as to whether they can be used in patients with concomitant autoimmune or auto-inflammatory diseases. Their usage can lead to the development of autoimmune phenomena known as immune related adverse events (irAEs), virtually affecting every organ. As the use of ICIs is drastically increasing, evidence of irAEs has been accumulating. Herein, we report a case of inflammatory myositis and arthritis 6 months after pembrolizumab therapy, an anti-programmed death-1 (PD1) ICI in a patient with lung cancer, aiming at raising awareness of the diagnostic and clinical challenges clinicians may face when checkpoint inhibitors-related rheumatologic irAEs are developed.