Myocarditis in idiopathic inflammatory myopathies: serologic and clinical correlates in a single-center registry.

To characterize the clinical and serological correlates of cardiovascular magnetic resonance (CMR)-confirmed myocarditis in idiopathic inflammatory myopathies (IIM), evaluate the diagnostic performance of high-sensitivity cardiac troponin I (hs-TnI), and quantify the independent prognostic impact of myocarditis relative to interstitial lung disease (ILD). Single-center retrospective cohort study (STROBE-compliant) of 142 consecutive adults with IIM (2019-2025). Myocarditis was confirmed by CMR according to the 2018 Lake Louise Criteria, performed both at diagnosis and during follow-up (with or without immunosuppression) upon clinical suspicion and/or elevated hs-TnI. Myositis-specific antibodies (MSA), myositis-associated antibodies (MAA), anti-Ro52 and antiphospholipid antibodies (aPL, Sydney criteria: ≥40 GPL/MPL units confirmed at ≥ 12 weeks) were systematically recorded. Associations were assessed with Fisher's exact test and logistic regression; multivariable models were pre-specified as parsimonious (two predictors) given the limited event count. Overall survival was analyzed with Kaplan-Meier curves, the log-rank test and Cox proportional-hazards regression. Myocarditis was confirmed in 9/142 patients (6.3%), without significant association with IIM class (P = 0.303) or with the antisynthetase antibody subgroup (anti-Jo-1 + PL-12 + PL-7 + EJ; 5.8% vs. 6.7%, P = 1.000). In univariable analyses, myocarditis was associated with Raynaud phenomenon (OR 13.6, 95% CI 2.3-80.0), aPL positivity (OR 10.7, 95% CI 2.6-43.9), anti-Ro52 coexisting with MSA/MAA (OR 8.7, 95% CI 2.2-34.8), anti-PM/Scl (OR 7.1, 95% CI 1.6-30.3), fever (OR 7.1, 95% CI 1.6-30.3) and ILD (OR 4.7, 95% CI 1.1-20.3). hs-TnI was markedly higher in myocarditis (median 366 vs. 3.5 ng/L; P < 0.001) with an area under the receiver-operating characteristic curve (AUROC) of 0.91 (95% CI 0.83-0.98). In the event-constrained multivariable model, Raynaud phenomenon (adjusted OR 13.1, 95% CI 1.5-112.7) and aPL (adjusted OR 7.2, 95% CI 1.4-36.0) remained independently associated. All-cause mortality was higher in myocarditis (44% vs. 9%; OR 7.95, 95% CI 2.0-31.5; log-rank P = 0.030; univariable Cox HR 3.77, 95% CI 1.03-13.78; P = 0.044), and persisted after adjustment for ILD in the logistic model (adjusted OR 5.9, 95% CI 1.3-26.1; P = 0.020), whereas ILD attenuated to a non-significant trend (adjusted OR 2.9, 95% CI 0.9-9.2; P = 0.073). In this single-center retrospective cohort, IIM-associated myocarditis was consistently associated with Raynaud phenomenon, aPL positivity and anti-Ro52 coexistence, and was associated with higher mortality than ILD. These findings support hs-TnI-guided triage to CMR as part of systematic cardiac surveillance in IIM, pending multicenter confirmation.