Hypereosinophilic syndromes are a group of disorders secondary to the accumulation of eosinophils leading to the injury of one or more organs. Among them, eosinophilic myocarditis (EM) is a rare form of inflammatory cardiomyopathy characterized by eosinophilic infiltration into myocardial tissue and subsequent release of substances with cell membrane damage and cell destruction. The degree of infiltration is thought to depend on the underlying condition, as well as the degree and duration of eosinophil exposure and ranges from mild localized disease to diffuse multifocal infiltrates associated with myocardial necrosis, thrombotic complications and endomyocardial fibrosis. The main causes of EM are hypersensitivity reactions, eosinophilic granulomatosis with polyangiitis, hypereosinophilic syndrome variants, infections and cancer. Clinical presentation can be variable, ranging from asymptomatic forms to life-threatening conditions, to chronic heart failure due to progression to chronic restrictive cardiomyopathy. Marked eosinophilia in peripheral blood, elevated serum eosinophilic cationic protein concentration and multimodality imaging may suggest the etiology of EM, but in most cases an endomyocardial biopsy must be performed to establish a definitive diagnosis. Systemic treatment varies greatly depending on the underlying cause, however the evidence of an eosinophilic infiltrate allows initiation of immunosuppressive therapy, which is the mainstay of treatment in idiopathic and in most forms of EM. Patients with helminthic infection benefit from anti-parasitic therapy, those with myeloid clone often need a tyrosine kinase inhibitor, while anticoagulant therapy should be undertaken in case of possible thrombotic complications.
