Case of isolated cardiac sarcoidosis diagnosed by newly developed abnormal uptake during serial follow‐up fluorine‐18 fluorodeoxyglucose positron emission tomography

Cardiac sarcoidosis (CS) causes lethal arrhythmia and heart failure and has a poor prognosis; therefore, early detection and early stage treatment are important. However, diagnosis of isolated CS may be difficult in some cases owing to the low sensitivity of myocardial biopsy. Herein, we describe the case of a patient with isolated CS, showing change from negative to positive fluorine‐18 fluorodeoxyglucose ((18)F‐FDG) positron emission tomography (PET) uptake results within 9 months. The patient showed rapid reduction in left ventricular systolic function with sustained ventricular tachycardia. The diagnosis of isolated CS is often under‐recognized in clinical practice because it commonly requires the diagnosis of extracardiac disease in the absence of a positive endomyocardial biopsy. The Japanese Circulation Society recently published guidelines for CS diagnosis stating that isolated CS can be clinically diagnosed with positive (18)F‐FDG PET or (67)Gallium result. In this case, serial follow‐up (18)F‐FDG PET was useful for diagnosing isolated CS.