Nivolumab-induced hypothyoidism with consequent hypothyroid related myopathy.

Purpose Nivolumab is a fully human IgG4 programmed death 1 immune checkpoint inhibitor (ICI) antibody that has anti-tumor activity by selectively blocking the interaction of the programmed death 1 receptor with its two known programmed death ligands PD-L1 and PD-L2. In doing so, this immune checkpoint inhibitor removes the negative signal stifling T cell activation and proliferation within the tumor microenvironment and demonstrates favorable antitumor activity. Case report We report an interesting case of immune checkpoint inhibitor-induced primary hypothyroidism with associated hypothyroid myopathy in a young patient with surgically resected stage IIIB melanoma receiving adjuvant nivolumab. He presented 12 weeks into therapy with severe myalgias, arthralgias, and intermittent disequilibrium of unclear etiology. Laboratory evaluation demonstrated a significant elevation in thyroid stimulating hormone and creatine kinase with an undetectable free T4 with standard laboratory measurement. With thyroid hormone replacement therapy alone, he had rapid improvement in his musculoskeletal symptoms and laboratory parameters over a three-week period. Discussion This case emphasizes the serious nature of endocrine immune-related adverse events in patients receiving immune checkpoint inhibitors. Additionally, it highlights that unlike most other immune-related adverse events, endocrine immune-related adverse events can generally be managed with adequate hormone replacement alone with swift improvements in symptoms. This allows patients to continue immune checkpoint inhibitors safely without immunosuppression which may dampen the anti-tumor activity of these agents. Conclusion This case highlights the importance of early recognition and the appropriate management of endocrine immune-related adverse events to maximize patient safety and good outcomes.