Direct Comparison of 67Ga-Scintigraphy and Fluorodeoxyglucose Positron Emission Tomography for the Evaluation of Cardiac Sarcoidosis.

BACKGROUND: 67Ga scintigraphy and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) are useful tools for diagnosing cardiac sarcoidosis (CS). However, its comparative diagnostic and prognostic values remain unclear. OBJECTIVES: This study aimed to assess the positivity rates, clinical characteristics, and prognosis of patients with CS who underwent both 67Ga scintigraphy and FDG-PET. METHODS: We retrospectively studied 512 patients with CS who were enrolled in the ILLUMINATE-CS (ILLUstration of the Management and prognosIs of JapaNese PATiEnts with CS) registry. Among them, 101 patients who underwent both 67Ga scintigraphy and FDG-PET before immunosuppressive drug administration were analyzed. Myocardial segments showing uptake on 67Ga scintigraphy and FDG-PET/computed tomography were semiquantified using the American Heart Association's 17-segment model. RESULTS: The median age was 63 (56-70) years, 64 (63.4%) patients were female, and the median left ventricular ejection fraction was 48 (38-59)%. The patients were divided into 4 groups based on the findings of both examinations: 1) both-positive (n = 26, 25.7%); 2) only FDG-PET-positive (n = 72, 71.3%); 3) only 67Ga scintigraphy-positive (n = 0, 0%); and 4) both-negative (n = 3, 3.0%). Among the FDG-PET-positive patients, only 26 (26.5%) showed uptake on 67Ga scintigraphy. Conversely, 94.0% of the segments that showed uptake on 67Ga scintigraphy were also identified as positive segments on FDG-PET. During a median follow-up of 2.9 (1.4-5.3) years, the composite outcome of all-cause death, hospitalization for heart failure, and fatal ventricular arrhythmia showed no significant difference between patients in the both-positive group and those in the only FDG-PET positive group. CONCLUSIONS: 67Ga scintigraphy demonstrates lower sensitivity for detecting myocardial inflammation in CS than FDG-PET and has limited prognostic significance.