Prognostic implications of residual cardiac FDG uptake in stable cardiac sarcoidosis post-immunosuppressive therapy

Background Cardiac sarcoidosis (CS) can cause irreversible left ventricular dysfunction and life-threatening arrhythmias, requiring early detection. FDG-PET/CT (18F-fluorodeoxyglucose-positron emission tomography/computed tomography) is crucial for diagnosing CS, but its prognostic value remains debated. Objective To assess the prognostic significance of residual cardiac FDG uptake in patients with CS during the stable phase following immunosuppressive therapy. Methods We retrospectively examined patients who underwent FDG-PET/CT at least 12 months after immunosuppressive therapy between June 2013 and October 2023. Cardiac metabolic activity (CMA) was quantitatively assessed to evaluate residual myocardial FDG accumulation. Major adverse cardiac events (MACE), including cardiac death, sustained ventricular arrhythmias, implantable cardioverter–defibrillator activation, hospitalization for heart failure, and cardiac function decline, were examined. Results Short-term (2-year) MACE incidence was higher in patients with residual uptake (P=0.030), whereas long-term (median 4 years) outcomes showed no significant difference (P=0.52). Among patients with left ventricular ejection fraction (LVEF) ≥ 50%, annual cardiac event rates remained low and similar (1.4% vs. 1.1%, P=0.67). In 23 patients with residual FDG uptake who had repeat FDG-PET without intensified therapy, uptake resolved in 8. Compared with the first CMA, follow-up CMA in 41 patients with repeat scans showed a significant decrease (median CMA: 3.63 to 0.71, P=0.038). Conclusions Residual cardiac FDG uptake is associated with increased short-term cardiac events but has limited impact on long-term outcomes. Residual uptake may spontaneously resolve in some patients without intensified therapy. These findings highlight the need to consider LVEF and the dynamic nature of FDG uptake in therapeutic strategy.