AbstractObjectiveMyocardial involvement is frequently observed in polymyositis (PM) and dermatomyositis (DM) but typically remains subclinical. This study aimed to investigate characteristics of myocardial involvement and compare differences between patients with PM and DM by cardiac magnetic resonance (CMR) imaging.MethodsFrom March 2017 to December 2019, a total of 17?PM and 27?DM patients were enrolled in this retrospective study. In all patients, clinical assessment and CMR examination were performed. CMR parameters, including left ventricular (LV) morphologic and functional parameters and CMR tissue characterization imaging parameters, such as native T1, T2, extracellular volume (ECV), and late gadolinium enhancement (LGE) were analyzed.ResultsPatients in both PM and DM groups, elevated global native T1 and ECV values were observed. Global ECV values were higher in the PM group when compared to the DM group (33.24 ± 2.97% vs. 30.36 ± 4.20%; P = 0.039). Furthermore, patients in PM and DM groups showed a different positive segment distribution of LGE, native T1 and ECV, whereas the number of positive segments in PM patients was greater compared to that in DM patients. No significant differences in LV morphological and functional parameters were observed between patients in PM and DM groups and most were in normal range.ConclusionCMR tissue characterization imaging could detect early myocardial involvement in PM and DM patients without overt LV dysfunction. Furthermore, characteristics of myocardial involvement were different between PM and DM patients with more serious seen in PM patients.