Interpretation of myocardial FDG uptake during corticosteroid therapy in cardiac sarcoidosis evaluation with 18F-FDG PET/CT

PURPOSE: F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is highly sensitive for detecting myocardial inflammation. However, corticosteroid therapy may alter myocardial metabolism, complicating the interpretation of FDG PET. This study aimed to evaluate the impact of corticosteroid therapy on physiological myocardial FDG uptake and assess the utility of fasting plasma glucose (FPG) and free fatty acids (FFA) in distinguishing physiological from pathological uptake. MATERIALS AND METHODS: We retrospectively analyzed FDG PET/CT scans of 40 CS patients who underwent paired scans before and after corticosteroid therapy, following prolonged fasting (> 18 h). The frequency of physiological myocardial FDG uptake was compared, and FPG and FFA levels were assessed as predictors using receiver operating characteristic (ROC) analysis. Exploratory analyses were also performed to assess metabolic changes across different levels of corticosteroid exposure. RESULTS: Physiological myocardial FDG uptake significantly increased after corticosteroid therapy (from 2.5% to 15%, P = 0.048). Post-treatment FFA levels were significantly lower, while FPG levels were higher. An FFA cutoff of 615 µEq/L predicted physiological uptake with 100% sensitivity and 83.6% specificity (AUC = 0.96, P < 0.001), whereas FPG showed poor discrimination (AUC = 0.43, P = 0.83). Patients with physiological uptake had significantly lower FFA levels; FPG did not differ between groups. In analyses stratified by corticosteroid dose, physiological uptake was less frequently observed at lower dose levels, accompanied by relatively preserved metabolic parameters. CONCLUSION: Corticosteroid therapy increases physiological myocardial FDG uptake in CS patients, likely due to reduced FFA levels and altered metabolism. FFA may serve as a useful marker for distinguishing physiological FDG uptake from abnormal uptake, supporting more accurate PET interpretation during corticosteroid therapy.