Amyopathic dermatomyositis associated with immune checkpoint inhibitor therapy in lung adenocarcinoma: a case report

Immune checkpoint inhibitors (ICIs) have proven efficacious in various types of cancers, including lung cancer, but they usually lead to a set of organ-specific immune-related adverse events (irAEs). In particular, checkpoint inhibitor pneumonitis (CIP) requires special attention because it is difficult to diagnose and can be potentially fatal. Accumulating real-world epidemiological data indicate that CIP is more common than previously reported. Amyopathic dermatomyositis (ADM), which shows no or minimal muscle damage, is positive for anti-melanoma differentiation-associated gene 5 (anti-MDA5) and involves unique skin findings, as well as clinical features of rapidly progressive interstitial lung disease (RP-ILD). Therefore, knowing how to differentiate between CIP and ADM-related RP-ILD is important, which can provide valuable experience for subsequent treatment of patients.

We report a case of a patient with stage IV lung adenocarcinoma who developed ADM associated with RP-ILD following the administration of pembrolizumab, an inhibitor of the programmed cell death 1 (PD-1) pathway. The principal adverse reactions to pembrolizumab are irAEs. However, pembrolizumab-associated ADM has not been previously reported in clinical settings. The patient presented with atypical skin lesions and tested positive for anti-MDA5 antibodies, accompanied by severe acute ILD.

We believe this case represents a valuable clinical reference for the future management of irAEs caused by pembrolizumab and emphasizes the necessity of early screening for anti-melanoma differentiation associated protein 5 (MDA5) antibodies in patients with CIP presenting as RP-ILD.