Comparative evaluation of F-FLT and F-FDG for detecting cardiac and extra-cardiac thoracic involvement in patients with newly diagnosed sarcoidosis.

BACKGROUND

F-FDG PET has been used in sarcoidosis for diagnosis and determination of the extent of the disease. However, assessing inflammatory lesions in cardiac sarcoidosis using F-FDG can be challenging because it accumulates physiologically in normal myocardium. Another radiotracer, 3'-deoxy-3'-F-fluorothymidine (F-FLT), has been investigated as a promising PET tracer for evaluating tumor proliferative activity. In contrast to F-FDG, F-FLT uptake in the normal myocardium is low. The purpose of this retrospective study was to compare the uptake of F-FLT and F-FDG in the evaluation of cardiac and extra-cardiac thoracic involvement in patients with newly diagnosed sarcoidosis. Data for 20 patients with newly diagnosed sarcoidosis were examined. F-FLT and F-FDG PET/CT studies had been performed at 1 h after each radiotracer injection. The patients had fasted for at least 18 h before F-FDG PET/CT but were given no special dietary instructions regarding the period before F-FLT PET/CT. Uptake of F-FLT and F-FDG was examined visually and semiquantitatively using maximal standardized uptake value (SUVmax).

RESULTS

Two patients had cardiac sarcoidosis, 7 had extra-cardiac thoracic sarcoidosis, and 11 had both cardiac and extra-cardiac thoracic sarcoidosis. On visual analysis for diagnosis of cardiac sarcoidosis, 4/20 F-FDG scans were rated as inconclusive because the F-FDG pattern was diffuse, whereas no FLT scans were rated as inconclusive. The sensitivity of F-FDG PET/CT for detection of cardiac sarcoidosis was 85%; specificity, 100%; and accuracy, 90%. The corresponding values for F-FLT PET/CT were 92, 100, and 95%, respectively. Using semiquantitative analysis of cardiac sarcoidosis, the mean F-FDG SUVmax was significantly higher than the mean F-FLT SUVmax (P < 0.005). Both F-FDG and F-FLT PET/CT studies detected all 24 extra-cardiac lesions. Using semiquantitative analysis of extra-cardiac sarcoidosis, the mean F-FDG SUVmax was significantly higher than the mean F-FLT SUVmax (P < 0.001).

CONCLUSIONS

The results of this preliminary study suggest that F-FLT PET/CT can detect cardiac and extra-cardiac thoracic involvement in patients with newly diagnosed sarcoidosis as well as F-FDG PET/CT, although uptake of F-FLT in lesions was significantly lower than that of F-FDG. However, F-FLT PET/CT may be easier to perform since it requires neither prolonged fasting nor a special diet prior to imaging.