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Myositis-Myocarditis Overlap — SCE Medical Oncology MCQ

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HardOncological EmergenciesMyositis-Myocarditis OverlapSCE Medical Oncology

A 55-year-old man with metastatic melanoma on nivolumab + ipilimumab develops acute onset of bilateral proximal leg weakness, myalgia and dark urine. CK is 15,000 IU/L. Troponin is 200 ng/L. What is the diagnosis and why is urgent cardiac assessment critical?

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Correct answer: A — Immune-related myositis — urgent cardiac assessment because ICI myositis overlaps with myocarditis in ~25% of cases (myositis-myocarditis overlap syndrome)

ICI-induced myositis can overlap with myocarditis (myositis-myocarditis overlap syndrome) in approximately 25% of cases, and with myasthenia gravis in a triple-overlap syndrome. Elevated troponin in the context of ICI-myositis mandates urgent cardiac assessment (echocardiogram, cardiac MRI, serial troponin). Mortality of the overlap syndrome exceeds 30%. Treatment requires immediate ICI cessation, high-dose IV methylprednisolone (1 g/day × 3-5 days), and ICU admission. IVIG/plasma exchange may be needed for refractory cases.

Reference: ESMO 2024 irAE Management Guidelines; Anquetil et al Medicine 2018