Objective The purpose of this study was to evaluate the cardiac sarcoidosis (CS) activity according to the classified visual uptake pattern using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) and assess the uptake pattern based on the free fatty acid (FFA) levels.
Methods Nineteen CS subjects who underwent ¹⁸F-FDG PET/CT examinations with heparin loading (HL) were recruited to evaluate their CS activity. The ¹⁸F-FDG uptake in the heart was classified into five categories ("none," "diffuse" and "diffuse at base," regarded as stable CS, and "focal" and "focal on diffuse," regarded as de novo or worsening CS). The subject data were compared with the ¹⁸F-FDG PET/CT findings in 13 healthy volunteers. The FFA serum levels were assessed in 10 patients with CS and all volunteers.
Results The sensitivity and specificity of ¹⁸F-FDG PET/CT with HL were 75% (6/8) and 73% (8/11), respectively. The major pattern of cardiac ¹⁸F-FDG uptake was "diffuse at base." Ten of the 32 subjects, including the control group, exhibited this pattern. The FFA serum levels before heparin administration were statistically significantly different between the patients with the "none" pattern and those with the "diffuse" and "diffuse at base" patterns. There were no significant correlations between the FFA serum levels after heparin administration and the ¹⁸F-FDG uptake patterns.
Conclusion "Diffuse at base" is the major ¹⁸F-FDG uptake pattern associated with inadequate physiologic ¹⁸F-FDG suppression. This pattern should be carefully interpreted when examining the ¹⁸F-FDG PET/CT images of CS patients. Additionally, increased FFAs levels associated with HL may not completely suppress the physiologic myocardial FDG uptake.