Abstract:

Objective To investigate the clinical characteristics of immune checkpoint inhibitor-associated myocarditis complicated by myositis, improve clinicians’ awareness of this condition, and reduce the rates of misdiagnosis and missed diagnosis. Methods The clinical data of one patient with immune checkpoint inhibitor-associated myocarditis complicated by myositis were retrospectively analyzed, and the relevant literature was reviewed. Results The patient was a 64-year-old man diagnosed with stage ⅢB squamous cell carcinoma of the right lung. After one cycle of tislelizumab combined with chemotherapy, on day 31, he developed acute fulminant myocarditis complicated by myositis, manifested by marked elevation of cardiac enzymes (peak troponin Ⅰ, 3.398 μg/L), third-degree atrioventricular block, and type Ⅱ respiratory failure. Following comprehensive treatment with high-dose methylprednisolone pulse therapy (1 g/d×3 d) combined with intravenous immunoglobulin (20 g/d×5 d), temporary cardiac pacing, and noninvasive ventilatory support, the patient gradually improved. As of February 2026, no recurrence of myocarditis or myositis had been observed, and tumor control remained stable. Conclusion Immune checkpoint inhibitor-associated myocarditis complicated by myositis is a rare and life-threatening complication of immunotherapy, characterized by rapid progression and high mortality. Early recognition and diagnosis, together with timely and potent immunomodulatory therapy, are critical for saving lives and improving outcomes.

Key words: myocarditis, myositis, immune checkpoint inhibitors, lung squamous cell carcinoma, immune-related adverse events