A case of giant cell myocarditis mimicking cardiac sarcoidosis successfully maintained by prednisolone and tacrolimus.

A 45-year-old woman with no medical history underwent pacemaker implantation for a symptomatic complete atrioventricular block. On day 6, she noticed diplopia and then fever, general malaise, and elevation of serum creatinine kinase (CK). She was transferred to our hospital on day 21. Serum CK was elevated to 4543 IU/L, and echocardiography revealed a left ventricular ejection fraction of 43 %. We diagnosed her with giant cell myocarditis (GCM) via an emergent myocardial biopsy that revealed a proliferation of lymphocytes, eosinophils, and giant cells without granulomas. Initial treatment with high doses of intravenous methylprednisolone and immunoglobulin improved her symptoms in a few days, and prednisolone was given as follow-up treatment. CK was normalized in a week and a thinning of the interventricular septum mimicking cardiac sarcoidosis (CS) occurred. On day 38, we added a calcineurin inhibitor, tacrolimus, and maintained her with a combination of prednisolone and tacrolimus at a target dose of 10-15 ng/mL. Six months after the onset, there were no signs of relapse despite the persistent mild elevation of troponin I levels. We present a case of GCM mimicking CS successfully maintained by a combination of two immunosuppressive agents. Learning objective: Recommended treatment for giant cell myocarditis (GCM), a potentially fatal disease, is a combination of three immunosuppressive agents. However, GCM shares many characteristics with cardiac sarcoidosis (CS), which is treated using prednisolone alone in many cases. Recent studies on GCM and CS suggest they are different spectrums of a common entity. Although they can clinically overlap, they have different progressive speeds and severities. We present a case of GCM mimicking CS successfully treated with a combination of two immunosuppressive agents.