Uptake of 18F-fluorodeoxyglucose (FDG) and 11C-methionine (Met) in mediastinum and hilar lymph nodes was studied using PET in 31 patients with sarcoidosis. The aim of our study was to examine whether these different tracers play a differential role in clinical assessment of pulmonary involvement.
Methods: Fluorine-18-fluorodeoxyglucose and 11C-Met PET were administered on different days. The differential absorption ratio of these tracers was calculated for the region of interest with the highest level of activity. Clinical reassessment of sarcoidosis was made at least 1 yr after the first PET examination. In seven patients whose lymph nodes still remained visible by other imagings at the time of reevaluation, the same PET study was performed again.
Results: Both FDG and Met were accumulated in the lymph nodes in all but one patient. The FDG and Met uptake ratios in all patients were not correlated, but they could be divided into the FDG-dominant group (FDG/Met uptake ratio > or = 2) and the Met-dominant group (FDG/Met uptake ratio < 2). Within each group, the FDG and Met uptake values were correlated. The rate of improvement assessed by clinical status and chest radiographs was considerably higher in the FDG- (78%) than in the Met-dominant group (33%). In the seven patients of the repeated PET examination, their FDG/Met uptake ratios were generally unchanged after 1 yr.
Conclusion: The results suggest that the FDG/Met uptake ratio using PET may reflect the differential granulomatous status in sarcoidosis and be a useful tool for pretreatment evaluation.