Steroid therapy affects the cardiac metabolic shift and requires the careful attention in evaluation of the cardiac sarcoidosis with FDG PET/CT

Objectives Cardiac sarcoidosis (CS) is a potentially life-threatening disease and the accurate diagnosis is important in patients with sarcoidosis. 18F-fluorodeoxyglucose (FDG) PET/CT plays an important role to detect active cardiac involvement and to evaluate the response to steroid therapy. However, physiological FDG uptake due to inappropriate pretest preparations such as a shorter fasting period, carbohydrate intake prior the scan or individual metabolic status could disturb an accurate imaging interpretation. Recently, we reported the usefulness of the long fasting with low-carbohydrate diet (LCD) preparation for suppressed physiological myocardial FDG uptake. However, the steroid therapy interferes with glucose metabolism and increases insulin resistance, therefore it may affect myocardial FDG uptake. Limited studies were reported about the effects of the steroid therapy on FDG PET/CT. Our first aim of this study was to examine the effect of the steroid therapy on physiological cardiac FDG uptake. Thus, we compared FDG PET/CT between before (1st scan) and after (2nd scan) the steroid therapy. The second aim was to evaluate the interactions between the physiological FDG uptake and plasma free fatty acid (FFA), fasting plasma glucose (FPG) and immunoreactive insulin (IRI) levels.

Methods Twenty-one patients (58.2 ± 15.0 years old, 8 male) who diagnosed as CS by Japanese Ministry of Health and Welfare were enrolled in this study. All patients were fasted over 18 hours with LCD the last night prior to the scan. Sixty minutes after FDG administration, a static scan was performed. Two experienced cardiac imaging physicians determined whether the uptake was physiological or not independently with the information of the MRI and myocardial perfusion images.

Results There was no discordant in the results of each physician. There was no patient who showed the physiological uptake at the first scans. However, 5 of the 21 patients (23.8 %) showed the physiological uptake at the 2nd scans. The fasting time and injection dose were not significantly different between two scans. There was no significant difference in FPG (86.6 ± 10.4 vs. 93.3 ± 17.6 mg/dl, p = 0.24), however, FFA was significantly lower (896.9 ± 295.1 vs. 677.2 ± 303.7 μEq/L, p = 0.01), and IRI was significantly higher (2.8 ± 2.3 vs. 4.6 ± 3.2 μU/mL, p = 0.02) at the 2nd scans compared to the 1st scans. In particular at the 2nd scans, the FFA level of the patients with physiological uptake was significantly lower than those without physiological uptake (762.8 ± 281.2 vs 403.2 ± 203.6 μEq/L, p = 0.02). The FFA level of the patients with physiological uptake at the 2nd scans tended to be lower FFA level at the 1st scan (951.1 ± 300.3 vs. 723.6 ± 218.7 μEq/L, p = 0.10).

Conclusions After the steroid therapy, long-fasting and LCD preparation could not perfectly suppress physiological FDG uptake in the cardiac region due to metabolic shift. We should pay the attention to evaluate the LV FDG uptake after the steroid therapy, in particular, for the patients with the lower FFA level at the scan before steroid therapy. $$graphic_D2DE9D65-6F69-492E-87F0-CC686BB50D0C$$