Immune-Related Myocarditis Presenting as Upper Abdominal Discomfort in a Patient With Metastatic Subungual Melanoma Treated With Nivolumab

Immune checkpoint inhibitors (ICIs) have transformed the treatment of advanced melanoma, but they are associated with immune-related adverse events, including myocarditis, which, although rare, can be life-threatening. We report a case of suspected nivolumab-induced myocarditis in a 76-year-old woman with metastatic subungual melanoma. After receiving two doses of nivolumab, she experienced mild upper abdominal discomfort without chest pain or dyspnea. Laboratory tests revealed elevated creatine kinase and troponin T levels, and subsequent ECG showed new negative T waves. Although cardiac MRI and biopsy were not performed, the diagnosis was clinically suspected based on biomarker elevation, ECG changes, and the exclusion of coronary artery disease. High-dose corticosteroid therapy was initiated, leading to normalization of biomarkers and resolution of ECG abnormalities. The patient recovered without recurrence. This case emphasizes the importance of early recognition and treatment of ICI-related myocarditis, even in patients with rare melanoma subtypes and atypical presentations.