Medical Student SHSU-COM Houston, Texas, United States
Disclosure(s):
Sarib M. Sultan: No financial relationships to disclose
Background: Eosinophilic myocarditis (EM) is a rare inflammatory cardiomyopathy characterized by myocardial eosinophilic infiltration, often linked with eosinophilic granulomatosis with polyangiitis (EGPA) or hypereosinophilic syndrome (HES). Corticosteroids remain first-line therapy, yet relapse and steroid-refractory disease are common. Interleukin-5 (IL-5) blockade with mepolizumab has emerged as a potential targeted option.
Methods: A structured narrative synthesis was performed on all published case reports and small series describing mepolizumab use in biopsy- or clinically confirmed EM. A comprehensive PubMed and JACC search were conducted from database inception through 2025, to identify all eligible reports. Data were extracted on etiology, dosage, follow-up, cardiac recovery, relapse prevention, and adverse events to compare outcomes against conventional management.
Outcome: Across twelve patients (seven reports), mepolizumab (100–300 mg subcutaneously every four weeks) was associated with improvement or stabilization of left ventricular ejection fraction (35–60%), marked eosinophil reduction, and successful corticosteroid tapering. No dose-dependent differences in outcomes could be determined, and dosing decisions were not standardized—most regimens were extrapolated from EGPA or asthma indications, based on clinician preference or severity of eosinophilia. Across all reports, no drug-related cardiac events or relapses were observed during 6–12 months of follow-up. The 2024 series additionally reported CMR resolution of myocardial inflammation in two patients, although imaging protocols remained inconsistent. Overall, evidence remains limited by the small number of cases, lack of controls, heterogeneous dosing, and non-standardized follow-up. Despite CMR being a well-established modality for myocarditis assessment, systematic use of LGE, T1, and T2 mapping was absent from most reports, reflecting a reporting gap rather than a true knowledge gap. Future studies should incorporate standardized CMR endpoints—including LGE burden, T1/T2 mapping, and edema/fibrosis resolution—to objectively characterize myocardial recovery and clarify treatment response to mepolizumab.
Conclusion: Mepolizumab shows promise in steroid-refractory or relapsing EM, particularly in EGPA/HES-associated cases, yet current evidence is limited to case-level observations. Prospective multicenter trials with standardized imaging and longer follow-up are essential to identify which EM phenotypes achieve sustained benefit from IL-5 blockade.
