Optimal Timing of Serial <sup>18</sup>F-Fluoro-2-Deoxyglucose Positron Emission Tomography after Prednisolone Treatment Introduction for Cardiac Sarcoidosis

Immunosuppressive therapy with prednisolone (PSL) is the first-line treatment for cardiac sarcoidosis (CS), and 18F-fluoro-2-deoxyglucose positron emission tomography (FDG-PET) is used to evaluate its efficacy to guide treatment. However, the appropriate timing of FDG-PET in CS remains unknown. This single-center, retrospective, observational study included 15 consecutive CS patients who underwent 3 serial FDG-PET scans (at baseline, in the early phase [1-2 months after PSL introduction], and in the late phase [k5 months after PSL introduction with a maintenance dose of PSL]). We adhered to the PSL tapering protocol by the Japanese Circulation Society even when early FDG-PET showed positive results (SUVmax k4.0). No patient died during the 908 (644-1600) days of observation. Negative results in the late phase were observed in 3 of 6 earlypositive patients, and 3 of 9 early-negative patients showed positive results in the late phase. Changes in echocardiographic parameters from baseline to the late phase were significantly better in late-negative patients than in late-positive patients (left ventricular end-diastolic diameter: -0.7 (-9.3-[-0.5]) mm versus +3.5 (0.8-7.5) mm, P = 0.039; left ventricular end-systolic diameter: -4.2 (-6.9-[-0.1]) mm versus +5.1 (0.5-7.0) mm, P = 0.015; left ventricular ejection fraction: +4.7% (-1.0-9.0%) versus -1.5% (-11.3-1.5%), P = 0.045)), although early FDG-PET did not predict those consequent changes. An interval of k5 months after introducing the PSL with a maintenance dose of PSL is long enough for FDG-PET to reflect consequent left ventricular functions, while an interval of 1-2 months can be too short.