Background Ultrasonography (US) is a useful modality that can directly visualize RA joint inflammation. Recently, brightness of thickened synovium is considered to associate with local synovitis. However the accuracy of US findings with the local pathophysiology remains uncertain since synovial biopsy could be heterogeneous depending on the biopsy site and can be influenced by various medications. On another front, synovial fluid (SF) is homogenous, easy to access and contains abundant inflammatory cytokines and growth factors, which play an important role in the local pathogenesis of RA. However, the association between SF proteins and joint US findings is not clear.
Objectives To clarify whether synovitis detected by US including synovial hypertrophy, vascularity and brightness reflect local joint molecular pathophysiology.
Methods Forty-four RA patients were recruited. All patients were performed standardized US examination of knee joint. US images were evaluated by semi-quantitative scoring (synovial hypertrophy; grey scale (GS) US, vascularity; power Doppler (PD) US) and quantitative analysis by using Image J (National Institutes of Health, MD, Maryland USA). The average of the pixels of synovial tissue area (GS quant), PD signal area (PD quant) and mean gray values of synovium (Brightness) in 3 areas of the knee joint were calculated. US guided SF aspiration was performed on the same day and concentrations of cytokines and growth factors were measured by Cytometric Beads Array. (BD Biosciences, NJ, USA)
Results Median age, disease duration and DAS28-ESR were 64 years, 1.5 years and 5.2 respectively. Mean GSUS and PDUS were 2.3 and 2.0. Nineteen patients were untreated. US inflammatory findings especially PD quant were well correlated with corresponding SF IL-6, IL-8, IL-1β and IL-10.(range of rho;0.40–0.72, p<0.05) synovial brightness also inversely correlated with SF VEGF (rho=-0.41, p<0.05). When we analyzed untreated and treated RA patients separately, GS quant did not correlate with any SF cytokines in treated group although, PD quant and brightness both significantly correlated with SF IL-6 and VEGF (p<0.05). Next, we divided the treated patients into 4 groups according to median of brightness and GS quant to compare the SF IL-6 levels. This analysis showed that SF IL-6 levels were influenced by synovial brightness rather than its hypertrophy. (p<0.05)
Conclusions Our results suggest that not only US PD signals but also synovial brightness is a useful indicator for joint inflammation rather than synovial hypertrophy itself in treated RA patients.
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Kelly S et al. Arthritis Res Ther. 2015 Mar 13;17:58.
Disclosure of Interest None declared