Complex cardiac overlap: immune checkpoint inhibitor myocarditis in hypertrophic obstructive cardiomyopathy with subsequent NSTEMI

Immune checkpoint inhibitor (ICI)–associated myocarditis is a rare but life-threatening complication, particularly challenging to diagnose in patients with coexisting cardiac conditions. A 58-year-old man with advanced oropharyngeal carcinoma treated with pembrolizumab presented with heart failure symptoms and markedly elevated troponin levels. Imaging revealed hypertrophic obstructive cardiomyopathy (HOCM) alongside cardiac magnetic resonance findings consistent with ICI-associated myocarditis. He initially responded to high-dose corticosteroids but relapsed due to non-adherence, requiring re-treatment and addition of mycophenolate mofetil. Following recovery, he developed a significant rise in troponin with new regional wall motion abnormalities. Coronary angiography demonstrated significant coronary artery disease, supporting the diagnosis of acute coronary syndrome in the context of the clinical presentation, biomarker elevation, and imaging findings, managed with percutaneous coronary intervention. Post-procedural hypotension was attributed to adrenal insufficiency and resolved with stress-dose corticosteroids. Follow-up imaging demonstrated features of both prior myocarditis and new ischemic injury. The patient improved clinically after PCI and was discharged with normalized troponin levels. This case highlights the diagnostic and therapeutic challenges of ICI-associated myocarditis in the presence of overlapping cardiac pathologies. Multimodality imaging and clinical context are essential for accurate diagnosis, and alternative causes of troponin elevation must be carefully excluded.