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Idiopathic inflammatory myopathies (IIM) can affect multiple organs, including the heart, potentially leading to arrhythmia, heart failure, and thereby a poor prognosis. We hypothesised that cardiac and skeletal muscle involvement in patients with IIM share pathological mechanisms, and that severe skeletal muscle involvement may be associated with cardiac involvement. The aim of this study was to identify disease-related parameters that indicate cardiac involvement in newly diagnosed patients with IIM.

In this prospective study, 34 newly diagnosed patients with IIM and 9 age- and gender-matched healthy controls underwent cardiac magnetic resonance imaging, blood analyses for skeletal muscle markers, and assessments of IIM-specific disease features.

Cardiac involvement was detected by cardiac magnetic resonance imaging in 47% of patients with newly diagnosed IIM, presenting as ongoing myocarditis/perimyocarditis (44%), ongoing pericarditis (25%) or previous myocarditis (31%). IIM patients with cardiac involvement had significantly more prevalent myositis (p=0.018) and higher levels of serum markers of muscle inflammation (myoglobin, p=0.039; alanine aminotransferase, p=0.045 and aspartate aminotransferase p=0.005) compared to IIM without cardiac involvement. IIM with ongoing myocarditis/peri-myocarditis displayed significantly elevated cardiac troponin I (cTnI) levels than IIM with ongoing pericarditis (p=0.015) or previous myocarditis (p=0.015). Additionally, cTnI levels were strongly correlated to myositis (as clinical manifestation, p=0.011), creatin kinase (p=0.001), myoglobin (p=0.001), lactate dehydrogenase (p=0.008) and aspartate aminotransferase (p=0.0.001).

Cardiac involvement as detected by cardiac magnetic resonance imaging is common at time of diagnosis in patients with IIM and is closely linked to the severity of skeletal muscle involvement.