Abstract
1170
Objectives: Rheumatoid arthritis (RA) is a disorder involving chronic inflammation of the synovial membrane that lines joints. Inflammation can be assessed using 18F-fludeoxyglucose (FDG)-PET/CT because inflammatory cells exhibit a high rate of glycolysis. Uptake of 18F-sodium fluoride (NaF), another PET tracer, shows osteoblastic activity and therefore bone involvement in joint disease. The aim of this study was to calculate the FDG and NaF mean standardized uptake value (SUVmean) in the hip joints of RA patients and to determine their association with patient characteristics.
Methods: FDG-PET/CT and NaF-PET/CT imaging was performed prospectively on 18 RA patients. The anatomical boundaries of the hip joint were defined as a rectangular region surrounding the entire head of the femur and its articulation with the acetabulum, excluding the femoral neck. More specifically, the lateral border of the rectangular region was defined as the distinction between the femoral neck and femoral head, the medial border was 2 mm lateral to the pelvic brim, and the superior and inferior borders were 1 cm superior and inferior to the edge of the femoral neck, respectively. A lower threshold of 150 HU and upper threshold of 1500 HU was applied to CT component of the coregistered PET/CT image, followed by morphological closing with an element radius of 20 to segment the skeletal structures within the anatomically defined region. The SUVmean was calculated separately for left and right hips on FDG-PET/CT and NaF-PET/CT images. Paired t-tests were used to determine differences in uptake between left and right hips. Linear regressions were used to compare averaged left and right PET parameters with clinical data.
Results: The FDG SUVmean was observed to be higher in the right hip compared to the left hip. No significant differences between right and left hip were observed in the global NaF SUVmean. FDG SUVmean was significantly inversely correlated with patient global visual analogue scale (VAS-PtGlobal) and Disease Activity Score in 28 joints (DAS28-CRP) (p = 0.0003 and p = 0.024, respectively). NaF SUVmean was significantly positively correlated with BMI and leptin (p = 0.023 and p = 0.009, respectively).
Conclusions: Uptake of FDG and NaF in the hip was found to be associated with clinical variables relevant to joint disease. In particular, FDG SUVmean was found to be inversely correlated with VAS-PtGlobal and DAS28-CRP while no significant correlation between either variable was found with NaF SUVmean. Significant positive associations were observed between NaF SUVmean and BMI and leptin, which could indicate increased joint degeneration at the hip resulting in increased NaF uptake. Future prospective studies are warranted to provide greater clarity regarding the utility of FDG and NaF in evaluating joint activity in RA.