BACKGROUND: Acute eosinophilic myocarditis (EM) is considered a highly lethal clinical condition, yet current knowledge relies largely on small case series. Robust data on its clinical presentation, associated conditions, management, and outcomes are lacking. METHODS: We conducted an international, multicenter, retrospective cohort study across 53 centers on five continents. Among 193 patients with histologically confirmed acute EM identified between 1992 and 2023, 156 met inclusion criteria after excluding cases with insufficient data, symptom duration >30 days, or unconfirmed pathology. RESULTS: Median age was 48 years (IQR 34–59), with a predominance of males (67%). Only two patients were ≤16 years. Dyspnea (76%), fever (61%), and chest pain (53%) were the most frequent presenting symptoms. Peripheral eosinophilia was only reported in 57%. Median left ventricular ejection fraction (LVEF) at presentation was 32% (IQR 25–48%). EM was associated with eosinophilic granulomatosis with polyangiitis (22%), hypersensitivity reactions (14%), idiopathic/undefined etiologies (45%), and miscellaneous causes (19%). In-hospital death or heart transplantation (HTx) occurred in 23 patients (15%), while 44% being treated with temporary mechanical circulatory support and 92% with immunosuppressive agents. One- and three-year cumulative rates of death or HTx were 19% and 24%, respectively. A higher—but not statistically significant—3‑year event rate was observed in hypersensitivity-related EM compared with EGPA-associated EM (46% vs. 13%; p=0.15). Increased age, decreased LVEF on admission and no immunosuppressive therapy during hospitalization were independent predictors of death or HTx. CONCLUSIONS: Acute EM frequently presents without peripheral eosinophilia, underscoring the essential role of endomyocardial biopsy for diagnosis. Despite contemporary management, in-hospital and mid-term mortality remain high. Effective patient-specific strategies to improve outcomes in this rare but life-threatening condition are needed.
Associazione Nazionale Medici Cardiologi Ospedalieri
