Discordant cardiac inflammation between 18F-FDG PET and CMR in patients with cardiac sarcoidosis

Current diagnostic criteria for cardiac sarcoidosis (CS) rely on non-invasive imaging tools including positron emission tomography (PET-CT) and cardiac magnetic resonance (CMR). The aim of this study was to assess the prevalence of discordant myocardial inflammation between PET-CT and CMR in patients with known cardiac sarcoidosis. We retrospectively identified patients with both ¹⁸F-FDG PET-CT and CMR who had histology-proven sarcoidosis (N = 148). Among these 25 (17%) had abnormal ¹⁸F-FDG metabolism with normal tissue characterization by CMR. Of these, 13 (9%) had the studies concomitantly within 180 days (median 5 days, IQR 1-31). During median follow up of 7 years, 3 (23%) deaths were documented. Although prospective studies are required to address the best imaging approach for cardiac inflammation, our observation that some patients with CS have evidence of disease activity on PET-CT, but not on limited CMR without mapping suggests that a negative limited CMR may not fully exclude CS.