Objectives To compare¹⁸f-Fluoro-Dexoxyglucose Positron Emission Tomography (FDG-PET/CT) findings in patients with polymyalgia rheumatica (PMR) and controls without rheumatologic disease.

Methods We have retrospectively included 50 patients with a diagnosis of PMR (EULAR/ACR criteria), who have had a FDG-PET/CT. For comparison, 53 patients who have had a FDG-PET/CT for initial staging or follow-up of neoplasm have been included as controls. 17 sites have been analyzed (2 shoulders, 2 acromio-clavicular and 2 sterno-clavicular joints, 2 greater trochanters, 2 hips, 2 ischial tuberosities, 2 iliopectinal bursitis, 2 pubic symphysis enthesis and only the interspinous space with the most FDG uptake). An FDG uptake score has been used (semi-quantitative scoring system, by Goerres and al. to evaluate visually FDG uptake (0 to 3 compared to liver uptake) into these sites. We calculated the FDG uptake score corresponding to the mean of intensity over all sites, and the number of sites with significant uptake (FDG uptake 2 or 3) for each patient. The cut offs for number of sites with high activity and for FDG uptake score were assessed using ROC curves and Odds Ratios.

Results The two groups were comparable for the median patient age (69.3 years for PMR vs. 68.1 for controls). Significant differences between the two groups were found for FDG uptake score (1.12 vs 0.34, p<0.00001) and for number of sites with significant uptake: 6.36 sites vs 1.49 sites, p<0.00001.

The presence of 3 or more sites with significant uptake was correlated with the diagnosis of PMR with 74% sensitivity, 79% specificity [OR =10.8]. For the FDG uptake score the cut off is 0.53 [Se 80%, Sp 77%; OR 13.6].

We found significant differences in all sites for FDG uptake score, and number of sites with significant uptake, particularly marked for shoulders, ischial tuberosities and interspinous bursitis (p<0.00001 for FDG uptake score).

Conclusions We found significant uptake in all sites studied in PMR compared to controls. We propose the number of 3 sites with significant uptake and a FDG uptake score superior at 0.53 for the diagnosis of PMR.

Disclosure of Interest None declared