Rapid-Onset Myositis and Myocarditis Following Dual Immune Checkpoint Inhibitor Therapy With Nivolumab and Ipilimumab for Gastric Adenocarcinoma: A Case Report.

Immune checkpoint inhibitors (ICIs) have revolutionized oncology by improving survival outcomes with fewer side effects than traditional chemotherapy. However, ICIs are associated with immune-related adverse events (irAEs) affecting various organ systems, including rare neuromuscular complications such as myositis and myocarditis. This report presents a 70-year-old male with gastric adenocarcinoma, Lynch syndrome, and other comorbidities who developed severe myositis and myocarditis, confirmed by MRI and enzyme testing, 11 days after his first cycle of nivolumab and ipilimumab. He initially showed improvement with high-dose steroids, but he declined further treatment. Due to his myositis, he suffered respiratory decline, cardiac dysfunction, and intensive care unit admission. Despite urgent plasma exchange and resumed steroid therapy, his condition did not improve, and care was transitioned to comfort measures to honor the patient's wishes. This case underscores the challenges in managing severe irAEs, particularly in steroid-refractory cases, where advanced immunosuppressive strategies may be needed. Early recognition of symptoms and multidisciplinary coordination are crucial for mitigating complications. As ICIs become more widespread, clinicians must remain vigilant for life-threatening irAEs and balance aggressive treatment with patient autonomy.