Eosinophilic Myocarditis: A Concise Review for Clinicians

Abstract Persistent eosinophilia can cause cardiac tissue damage, typically in the form of eosinophilic myocarditis, whether the underlying cause is reactive, a clonal myeloid disorder, or idiopathic hypereosinophilic syndrome (HES). Eosinophilic myocarditis (EM) ranges from mild localized disease to multifocal widespread infiltrates associated with myocardial necrosis, thrombotic complications and endomyocardial fibrosis. Systemic treatment varies widely depending on the underlying cause, so thorough investigation and precise diagnosis are essential. Evaluation includes assessment for reactive causes of eosinophilia (vasculitis such as EGPA/Churg-Strauss, parasitic infection, autoimmune disease, IgG4-related disease, medications and other causes), genetic lesions characteristic of clonal myeloid disorders (PDGFRα and PDGFRβ and FGFR1) and flow cytometry and molecular studies for the aberrant T-cells characteristic of lymphocyte-variant hypereosinophilic syndrome (L-HES). Patients with reactive eosinophilia require treatment for the underlying cause, such as anti-parasitic therapy for helminthic infection or immunosuppression for EGPA/Churg-Strauss. Those with a myeloid clone often benefit from the tyrosine kinase inhibitor imatinib. Steroids are first line treatment for idiopathic HES and L-HES and hydroxyurea or (pegylated) interferon-α may be used for relapsed or refractory disease. Mepolizumab, an anti-interleukin-5 monoclonal antibody, is an effective steroid-sparing agent in HES but is not widely available for this indication.