Successful Use of Ruxolitinib for Steroid-Refractory Immune Checkpoint Inhibitor–Associated Myocarditis

Immune checkpoint inhibitors (ICIs) can trigger life-threatening immune-related adverse events, including myocarditis. Steroid-refractory cases pose significant therapeutic challenges. A 57-year-old woman with metastatic non-small cell lung cancer developed fulminant myocarditis with bidirectional ventricular tachycardia and biventricular dysfunction after pembrolizumab therapy. Despite early high-dose corticosteroids, cardiac biomarkers remained elevated and arrhythmias persisted. Second-line agents (mycophenolate mofetil, intravenous immunoglobulin) were discontinued owing to adverse effects. Off-label ruxolitinib was initiated after interdisciplinary discussion. This led to sustained clinical improvement, return to sinus rhythm, and recovery of biventricular function. This case highlights the therapeutic challenges in steroid-refractory ICI-associated myocarditis. Ruxolitinib may offer a promising option in these settings, though prospective data are lacking. ICI-associated myocarditis can present with ventricular arrhythmia and heart failure. Ruxolitinib may be considered in steroid-refractory cases.