Impact of systemic immune-mediated diseases on clinical features and prognosis of patients with biopsy-proved myocarditis

Introduction: Myocarditis has been described in association with many systemic immune-mediated diseases (SIDs). However, the role of SIDs in influencing clinical presentation and outcome of patients with a new diagnosis of biopsy-proved myocarditis, has never been investigated so far. Methods: We enrolled 25 consecutive cases with biopsy-proved myocarditis in the context of SIDs, and controls with isolated myocarditis, matched 1:1 by age, gender, ethnicity and clinical presentation. All of the patients presented with acute symptoms, normal coronary arteries, and no previous history of myocarditis. Detailed diagnostic workup, including blood exams, echocardiogram, arrhythmia monitoring and cardiac magnetic resonance (CMR) were obtained at baseline and at defined time points, up to 12-month follow-up (FU). Results: At presentation, patients with SIDs had more commonly inflammatory biomarkers elevation, signs of associated pericarditis, and replacement fibrosis at histology, as compared to controls (18 vs. 6, 20 vs. 12, and 21 vs. 11, respectively; all p < 0.05). The Lake Louise criteria at CMR were negative in 19 vs. 10 patients with and without underlying SIDs, respectively (p = 0.021). Baseline ECG, in-hospital arrhythmia telemonitoring and echocardiographic findings were not significantly different between groups (all p = n.s.). At 12-month FU, the composite major endpoint of cardiac death, end-stage heart failure or malignant ventricular arrhythmias was significantly more common in cases than in controls (7 vs. 1, respectively, p = 0.049). Conclusion: In patients with a new diagnosis of myocarditis, the presence of underlying SIDs is associated with distinct baseline clinical features and a significantly worse 1-year outcome.