Discordance between site and expert-adjudicated myocarditis diagnosis using 2025 ESC criteria: insights from the Pre-MYO cohort

Introduction Myocarditis is an inflammatory disease with heterogeneous clinical presentations, making diagnosis challenging. The recently published 2025 European Society of Cardiology (ESC) guidelines provide standardized diagnostic criteria integrating clinical features, cardiac magnetic resonance (CMR), and endomyocardial biopsy (EMB). This study aims to review myocarditis diagnoses assessed by a clinical committee and compare them with local diagnoses in the Pre-MYO cohort. Methods The Pre-MYO cohort is a national, prospective, observational, multicenter registry (76 hospitals) including patients with suspected myocarditis. A clinical committee reviewed all cases using the 2025 ESC myocarditis diagnostic criteria, classifying them as definite myocarditis (based on CMR criteria and/or confirmation by endomyocardial biopsy [EMB]); possible myocarditis (at least one clinical symptom and one objective diagnostic finding); and unlikely/rejected myocarditis (clinical suspicion not supported by CMR or EMB or alternative diagnosis confirmed). Local diagnoses were assigned in situ according to contemporary clinical practice at each center. Results An expert review of 606 suspected myocarditis cases was conducted and compared with local diagnoses. In clinical settings (1,078 cases), 753 cases (69.9%) were confirmed as myocarditis, 85 (7.9%) as probable myocarditis, and 240 (22.3%) were ruled out. Among the expert-reviewed cases, fewer were considered definite myocarditis (52%; 49% confirmed by CMR and 3% by EMB), and more were classified as possible myocarditis (21.6%) (Figure 1A and 1B). Agreement was strongest at the extremes: 71% of cases originally diagnosed as confirmed myocarditis remained confirmed after review, and 88% of those initially considered unlikely or discarded stayed in that category. The intermediate category showed the greatest discordance: of cases first labeled as possible myocarditis, only 51% retained this label after committee review, while 23% were upgraded to definite myocarditis and 24% were reclassified as unlikely or discarded. Conclusion The study shows moderate discordance between local and expert-reviewed diagnoses, highlighting the need to disseminate clinical recommendations and establish consensus diagnostic criteria. This will ultimately enable the development of better-characterized cohorts for future studiesDiagnosis discordance of myocarditis