Identification of characteristics of overt myocarditis in adult patients with idiopathic inflammatory myopathies

Background: Myocarditis is a rare complication of idiopathic inflammatory myopathies (IIMs), which is usually underestimated because of limited applications of endomyocardial biopsy and cardiovascular magnetic resonance (CMR) in clinical routines. Methods: From January 2014 to January 2019, 62 patients with initial untreated IIMs were enrolled, including 31 cases with myocarditis (case group) and 31 cases without cardiac involvement (control group). Myocarditis secondary to IIMs was defined based on definitions of IIMs. All medical data were retrieved from electrical medical records of PUMCH. The differences between two groups in symptoms, serum levels of cardiac troponin I (cTnI), creatine kinase-isozyme and N-terminal pro-brain natriuretic peptide (NT-proBNP) were analyzed. The comparisons of arrhythmia, left ventricular ejection fraction (LVEF) and restrictive diastolic dysfunction between two groups were conducted in the analysis of electrocardiogram and electrocardiogram. Besides, CMR data were analyzed to explore the characteristics of CMR in the identification of myocarditis. Meanwhile, 31 patients with myocarditis were divided into two subgroups based on the activity of anti-mitochondrial antibody M2 (AMA-M2), and the differences between two subgroups in the above tests were also analyzed. Results: Compared with control group, patients with myocarditis exhibited shorter disease durations (defined as the period from onset symptoms of IIM to diagnosis of IIM), more symptoms associated with IIMs, more manifestations of heart failure, and higher frequency of positive AMA-M2 antibody (P<0.05). Patients with myocarditis exhibited elevated levels of cTnI, creatine kinase-isozyme and NT-proBNP compared with control group. In case group, the area under the curve indicating myocarditis for CK-MB, cTnI, and NT-proBNP was 0.654, 0.915 and 0.973, with optimal cut-off values of 24.4 mu g/L, 0.1 ng/L and 531 pg/L, respectively. Ventricular arrhythmia, atrial arrhythmia, abnormal Q wave and left anterior fascicular block (LAFB) were showed in 76.7%, 53.3%, 74.2% and 51.6% of patients in case group (P<0.01). Patients of case group were featured as decreased LVEF and restrictive diastolic dysfunction compared with control group (P<0.05). Analyzing CMR data of patients of case group, the basal segments (74.2%) and mid-cavity segments (71.0%) were the most frequently involved areas of late gadolinium-enhancement (LGE), while intramural LGE (54.8%) and subendocardial LGE (51.6%) were reported more commonly than subepicardial LGE (19.4%). In patients with myocarditis and positive AMA-M2 antibody, LVEF and right ventricular ejection factor (RVEF) were decreased, and more cases presented diffuse LGE than those with negative AMA-M2 antibody (P<0.05). Conclusions: Symptoms of heart failure and arrhythmias, elevated levels of cTnI and NT-proBNP, and positive AMA-M2 antibody play an important role in the identification of myocarditis in IIMs. Most frequently involved areas of LGE were found in the ventricular septal, basal and mid-cavity segments, as well as in the sub-endocardium and intramural myocardium. Diffuse LGE is common in the detection, which is correlated with AMA-M2 antibody in patients with myocarditis related to IIMs.