The newly developed Seaport criteria classify lymphocytic myocarditis on endomyocardial biopsy into mild, moderate, and severe grades using CD3 immunohistochemistry to provide more consistent and reproducible diagnoses, according to a recent study.
An international panel of cardiovascular pathologists from the Society for Cardiovascular Pathology and the Association for European Cardiovascular Pathology developed consensus criteria for the histopathologic diagnosis of lymphocytic myocarditis on endomyocardial biopsy. The new Seaport criteria, published in Cardiovascular Pathology, were created to address limitations of the Dallas and European Society of Cardiology guidelines, which have been inconsistently applied and have demonstrated limited reproducibility.
The Seaport criteria incorporate hematoxylin and eosin staining and CD3 immunohistochemistry to identify T lymphocytes. Myocarditis is classified into three grades of severity– mild, moderate, and severe – with an additional category termed scattered increased T lymphocytes of undetermined significance. Mild myocarditis is defined by either a single cluster of 5 or more lymphocytes, or at least 15 non-clustered CD3+ cells within the busiest high-powered field. Moderate myocarditis is diagnosed when two or more lymphocyte clusters are present, while severe myocarditis requires multifocal or diffuse lymphocytic infiltrates with myocyte injury. Myocyte injury is described by nuclear and cytoplasmic changes, including hypereosinophilia, karyorrhexis, karyolysis, and sarcolemmal scalloping, but this feature is not required for all diagnostic levels.
The consensus was reached through a 3-year Delphi process involving literature review, slide evaluations, surveys of practicing pathologists, and international meetings in Baltimore and Boston. The resulting framework was designed to provide standardized definitions that could be applied in multiple practice settings. Ancillary stains, such as CD68 for macrophages and Masson Trichrome for fibrosis, are recommended when appropriate, though only CD3 staining is required for classification.
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