Quantification of FDG uptake of the joints in rheumatoid arthritis and correlations with clinical disease activity using volumetric PET/CT parameters

Objectives Rheumatoid arthritis (RA) is a systemic inflammatory disease affecting small and large joints. Joint Inflammation is detectable with FDG-PET. The purpose of this study is to measure global FDG uptake in the joints of patients with RA and compare to clinical indices of disease activity

Methods Fifteen patients with RA underwent whole-body PET/CT. Joint inflammation was assessed by measuring FDG uptake using novel volumetric PET/CT indices such as metabolic active volume (MAV) and total lesion glycolysis (TLG=MAV×SUVmean). The association between global joints uptake with clinical measures of disease activity was performed using Spearman correlations

Results There were fifteen (male:11) patients with mean age of 56.5 (SD:12.9) and a median disease duration of 7.4 years. On average, composite disease activity scores were low [DAS28=3.74 (1.1)] although the median CRP level was modestly elevated at 1.2 (IQR 0.5,1.6). SUVmean (rho=0.76,p=0.001) and TLG (rho=0.70,p=0.004) strongly correlated with CRP level in 14 cases. TLG tended to correlate with total number of swollen joints (rho=0.369,P=0.17) whereas there was no correlation with subjective clinical measures of Patient Global Assessment scores (rho=-0.363,p=0.18) Physician Global Assessment scores (rho=0.134,p=0.633) or tender joint counts (rho=-0.281,p=0.310). Patients who were positive for anti-cyclic citrullinated peptide antibodies were more likely to have elevated PET measures (p=0.04)

Conclusions FDG uptake in inflamed joints correlates best with measures of systemic inflammation, seropositivity and objective evidence of joint swelling in RA while showing poor correlation with subjective measures of disease activity. Based on these preliminary data we believe approaches in this scientific communication will play a major role in assessing the activity of inflammatory joint disease in patients with RA