A case of cardiac sarcoidosis initially misdiagnosed as giant cell myocarditis and treatable by single steroid therapy

A 55-year-old woman was admitted due to palpitation and breathlessness arising from ventricular tachycardia with mild hypokinesia of the left ventricle. After conventional pharmacological therapy, she was relieved of her symptoms by the time of her discharge. Her electrocardiogram showed gradual prolongation of the PQ interval, finally leading to asymptomatic complete atrioventricular (AV) block after 1.5 years. The left ventricle showed severe hypokinesia with multiple aneurysmal deformities and extensive myocyte injury with inflammatory infiltrates in the endomyocardial biopsy specimen consisting of lymphocytes and multinucleated giant cells. After histological diagnosis of giant-cell myocarditis, a single steroid administration rapidly improved AV conduction. Considering the peculiar clinical figures such as the chronic progressive clinical course, cardiac conduction abnormalities, and marked effectiveness of single steroid therapy, close histological re-evaluation of the biopsy sample including immunohistochemical analyses was undertaken, and the conclusion was a diagnosis of cardiac sarcoidosis due to recognized granulomatous lesions with marked interstitial fibrosis. In clinical practice, we need to realize the usefulness of combined diagnostics methodology utilizing both histological and clinical evaluation in order to differentiate giant cell myocarditis from cardiac sarcoidosis.