Early cardiac magnetic resonance leads to diagnose the etiology of myocardial infarction with non-obstructive coronary arteries

A 56-year-old man who developed chest discomfort was referred to our hospital. He had no history of prior cardiac disease and allergies. The electrocardiogram revealed no ST-segment change. Echocardiogram demonstrated mildly reduced left ventricular ejection fraction with diffuse hypertrophy and regional asynergy in the inferior wall. Laboratory test showed elevated cardiac biomarker (cTnI: 5911.5 ng/L—reference <26.2 ng/L) with mildly increased eosinophils (609/µL, 7.1% of leukocytes). His coronary arteries were almost normal by coronary angiogram. Therefore, myocardial infarction with non-obstructive coronary arteries (MINOCA) was considered as a working diagnosis. Subsequently, cardiac magnetic resonance (CMR) was performed to investigate the etiology of MINOCA. Both native T1 and T2 mapping values and late gadolinium enhancement have indicated serious cardiac injury and oedema suggesting myocarditis (Panels 1A–1D). Surprisingly, there was a significant discrepancy between his mild symptoms and severity of findings following CMR. Endomyocardial biopsy was performed, the specimen showed cardiac injury...