OP0190 USEFULNESS OF 18F-FLUORODEOXYGLUCOSE POSITRON EMISSION TOMOGRAPHY IN DIAGNOSING POLYMYALGIA RHEUMATICA AND LARGE-VESSEL VASCULITIS: A CASE-CONTROL STUDY

Abstract

Background:Polymyalgia rheumatica (PMR) is a relatively common disease among the elderly. None of the most common imaging techniques provides diagnostic certainty of PMR. 18F-fluoro-dexoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) may be a useful candidate as it can be used to visualize articular and periarticular FDG uptake at different locations, as well as associated large-vessel vasculitis (LVV), but its usefulness needs to be evaluated in the absence of large-scale case-control studies.Objectives:The purpose of this study was to determine the usefulness of FDG-PET/CT in diagnosing PMR and LVV.Methods:We analysed FDG-PET/CT scans performed between January 2015 and December 2019 on patients diagnosed with PMR. For comparisons, patients with PMR were matched 1:1 to controls according to age and sex. FDG-PET/CT scans had been performed on controls over the same period for diagnosis of cancer-associated stroke. FDG uptake was scored visually using a semi-quantitative analysis (score 0-3) for 17 articular or periarticular sites, as described by Sondag et al. [1], and for 13 vascular sites, as described by Slart et al. [2]. The case and control groups were compared using generalized linear mixed models (binomial distribution, logit function) for binary outcomes, and linear mixed models for continuous outcomes, with matched sets as a random effect. The optimal threshold for the number of sites with significant hyperfixation (score ≥ 2) was determined by maximizing the Youden index.Results:81 patients with a diagnosis of PMR and 81 controls were included (mean (SD) age 70.7 (9.8) years; 44.4% women). We found significant differences between the PMR and control groups at all articular or periarticular sites for: 1) FDG uptake score (p<0.0001); 2) number of patients per site with significant FDG uptake (score ≥ 2) (p<0.0001); 3) global FDG articular uptake scores (score 0-51) (31 [IQR, 21 to 37] versus 6 [IQR, 3 to 10], p<0.001); and 4) number of sites with significant FDG uptake (score ≥ 2) (score 0-17) (11 [IQR, 7 to 13] versus 1 [IQR, 0 to 2], p<0.001). Using ROC curve analysis (Figure 1), we found that the presence of 6 or more sites with significant FDG uptake (≥ 2) was associated with the diagnosis of PMR with a sensitivity of 84% and a specificity of 96% (AUC 0.96 [95% CI 0.93-0.99]). No significant differences in global FDG vascular uptake scores (score 0-39) or in number of patients with at least 1 significant uptake vascular site (score ≥ 2) were found between the PMR and control groups (1 [IQR, 0 to 4] versus 4 [0 to 6], p=0.06 and 8 (11.3%) versus 10 (14.1%), p=0.62 respectively).Figure 1.ROC curve analyzing performance of FDG-PET/CT for the diagnosis of PMR according to the number of sites with significant FDG uptake (≥ 2)Conclusion:Our results demonstrate that the FDG uptake score and the number of sites with significant FDG uptake could be relevant criteria for the diagnosis of PMR. However, unlike other authors, we found no evidence suggesting that FDG-PET/CT may be useful in diagnosing silent underlying LVV in patients with isolated PMR.