Case report of elevation of high-sensitivity cardiac troponin T in the absence of cardiac involvement in immune checkpoint inhibitor-associated myositis.

Background: Immune checkpoint inhibitors (ICIs) have markedly improved outcome in various types of cancer. ICI-associated myocarditis is one of the most severe immune-related adverse events. In particular, high concentrations of cardiac troponin T (cTnT) are associated with a high risk of death and early detection and vigorous therapy with high-dose steroids may improve survival. However, chronic skeletal muscle disorders have been suggested as a non-cardiac source of elevated high-sensitivity cardiac troponin T (hs-cTnT) concentrations. Case summary: Here, we present the case of a 72-year-old patient with metastatic melanoma treated with nivolumab and ipilimumab, who developed symptomatic myositis [creatine kinase (CK) max. 3113 U/L]. Due to substantially elevated concentrations of hs-cTnT (max. 1128 ng/L, normal <14 ng/L, Elecsys), the patient was referred to the cardio-oncology unit for evaluation of concomitant myocarditis. The patient did not report any cardiac symptoms and there were no clinical signs of congestion or rhythm abnormalities. Concentrations of NT-proBNP were within the normal range. Echocardiography showed normal cardiac dimensions and normal systolic and diastolic function. Cardiac magnetic resonance imaging confirmed these findings and also showed no evidence of acute or post-inflammatory myocardial tissue changes. Absence of relevant cardiomyocyte injury was supported by determination of normal levels of cardiac troponin I concentrations and made endomyocardial biopsy in this severely ill patient unnecessary. Discussion: Our observation documents ICI-induced myositis as an alternative non-cardiac cause of hs-cTnT elevation. A global cardiologic approach employing clinical and cardiac magnetic resonance imaging data as well as NT-proBNP and cardiac troponin I helps to identify false positive hs-TnT elevation under ICI therapy.