Biopsy-Proven Eosinophilic Myocarditis With Nonconfirmatory Postcorticosteroid CMR in ANCA-Negative EGPA

BACKGROUND: Acute eosinophilic myocarditis is rare but potentially fatal; after corticosteroid initiation, systemic eosinophilia, myocardial injury, and cardiac magnetic resonance tissue markers may evolve on different timescales. CASE SUMMARY: A 66-year-old man with adult-onset asthma presented with palpable purpura, NYHA functional class III dyspnea, hypereosinophilia, myocardial injury, and left ventricular dysfunction. Coronary angiography showed no obstructive disease. Endomyocardial biopsy before pulse methylprednisolone confirmed necrotizing eosinophilic myocarditis; extracardiac findings supported antineutrophil cytoplasmic antibody-negative eosinophilic granulomatosis with polyangiitis. Postcorticosteroid cardiac magnetic resonance showed T1-based injury markers without detectable T2-based edema; revised Lake Louise criteria were not met. Eosinophils rapidly normalized, whereas high-sensitivity troponin T and N-terminal pro-B-type natriuretic peptide declined more slowly, and global longitudinal strain remained abnormal despite ejection fraction recovery. DISCUSSION: Early endomyocardial biopsy anchored the diagnosis before corticosteroids likely attenuated inflammatory and edema-sensitive signals. TAKE-HOME MESSAGE: Eosinophil clearance is not myocardial recovery.