Prevalence and early detection of myocarditis in idiopathic inflammatory myopathies: a prospective single-centre...

To determine the prevalence of myocarditis with newly diagnosed idiopathic inflammatory myopathy (IIM) and assess the utility of serum cardiac biomarkers as initial screening for myocarditis.

We prospectively enrolled patients with IIM at the Johns Hopkins Myositis Center between 7/1/2022-3/30/2023. Twenty-six patients underwent cardiac serum biomarkers, electrocardiography, and cardiac imaging (transthoracic echocardiogram and cardiac magnetic resonance imaging (CMR). Myocarditis was diagnosed with CMR using the 2009 Lake Louise Criteria. Clinical cardiac outcomes, including heart failure events, cardiac hospitalisation, and arrhythmia events were also assessed at follow-up.

27% (7/26) met the Lake Louise Criteria for myocarditis by CMR. Of patients found to have myocarditis, 71% (5/7) were symptomatic with dyspnoea on exertion, pleuritic chest pain, or with palpitations. The most common diagnosis among those with myocarditis was IIM/SSc overlap disease (5/7, 71%), and the most common antibody was Anti-Ku (3/7, 43%). When compared to patients without myocarditis, those with myocarditis more frequently had elevations in both troponin and NT-proBNP (100% vs. 42%, p=0.003) or an abnormal EKG (100% vs. 37%, p=0.004) with reduced ejection fraction on echocardiogram yielding a poor sensitivity with only 2/7 (29%) of patients with myocarditis demonstrating an EF of <50%.

Myocarditis occurred in 27% of this cohort, with IIM/SSc overlap being the most common subgroup. Anti-Ku was the most prevalent autoantibody, indicating a potentially higher risk for these patients. All had elevated cardiac biomarkers and abnormal EKGs, suggesting these could be useful for screening and further tests like cardiac MRI.