To present a rare case of immune checkpoint inhibitor (ICI) induced ocular myositis with respiratory involvement following pembrolizumab therapy, and to discuss the diagnostic challenges and management in this context.

Immune checkpoint inhibitors (ICIs), such as pembrolizumab, enhance immune response against cancer by targeting receptors like programmed death-1 (PD-1), programmed death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). However, these agents can cause immune-related adverse events (irAEs), affecting various organs, including nervous system and muscles. ICI-induced myositis is rare, with ocular involvement being exceedingly uncommon, affecting approximately 0.06% of patients. This case highlights the diagnostic and therapeutic complexities of ICI-induced ocular myositis.

A 62-year-old woman with a history of renal carcinoma was treated with first dose of pembrolizumab.  Starting approximately 30-days later, she presented with progressive symptoms including ophthalmoplegia, bilateral ptosis, dysarthria, dysphagia, dyspnea, and proximal muscle weakness. There was an initial concern for myasthenia gravis. Electrodiagnostic testing showed no decrement to repetitive stimulation, and electromyography showed features of proximal irritable myopathy. Anti-acetylcholine receptor (AChR) binding and anti-muscle specific kinase (MuSK) antibodies were negative. Imaging suggested extraocular muscle inflammation without significant structural changes. Given the respiratory involvement, the patient was treated with corticosteroid and intravenous immunoglobulin (IVIG), leading to gradual improvement in symptoms and CK levels.

ICI-induced ocular myositis is rare but serious irAE. Early recognition and differentiation from conditions such as myasthenia gravis (MG) are essential for appropriate management. This is particularly significant, as myocarditis and higher mortality rates have been more frequently associated with patients suffering from irMyositis compared to those with irMG. In cases of severe involvement, such as cardiac and respiratory compromise, the combination of corticosteroids and IVIG may be necessary for optimal outcomes. Long-term monitoring is important, as immunosuppressive therapies may be required for extended periods to manage persistent symptoms and prevent recurrence.