Complete remission of giant cell myocarditis by prednisolone monotherapy: A case with mild inflammation demonstrated by mismatch between T2-high intensity areas and late gadolinium enhancement.

Unlabelled: Giant cell myocarditis (GCM) is a potentially lethal subtype of myocarditis. Herein, we report a case of a 22-year-old woman with GCM who was successfully treated with prednisolone monotherapy. The patient had a fever and shortness of breath and was referred to our hospital. Laboratory test results revealed elevated troponin I levels. Cardiac magnetic resonance (CMR) showed high intensity in the inferoseptal segment of the left ventricle on T2-weighted short tau inversion recovery imaging without late gadolinium enhancement (LGE), suggesting predominant edema rather than necrosis. The patient was diagnosed with GCM based on an endomyocardial biopsy, which revealed lymphocyte infiltration and multinucleated giant cells in the absence of granuloma formation. Subsequently, the patient received intravenous methylprednisolone at 1000 mg/day for 3 days followed by oral prednisolone at 30 mg/day, which normalized troponin levels. Follow-up CMR revealed improved cardiac inflammation; therefore, the patient was discharged without prescribing another immunosuppressive agent. Prednisolone was tapered and terminated three years after discharge. The patient went one year without medication and had no recurrence of GCM on follow-up. This case highlights the presence of mild GCM, successfully treated by steroid monotherapy, in which the mismatch between high-intensity T2 areas and LGE suggests mild inflammation.

Learning Objective: Giant cell myocarditis (GCM) is potentially lethal and usually requires multiple immunosuppressive agents. Here, we report a patient with GCM with preserved left ventricular ejection fraction. Cardiac magnetic resonance revealed focal high T2 signal intensity areas without late gadolinium enhancement, indicating myocardial edema without necrosis. The patient remained in remission with prednisolone monotherapy for 2 years. Our report indicates that "mild" GCM may be treated with prednisolone monotherapy.