Plasma IL-6 levels correlate with clinical and ultrasound measures of arthritis in patients with systemic lupus erythematosus

Objective The objective of this paper is to elucidate the role of specific cytokines in lupus (SLE) arthritis. Methods Fifty SLE and 40 RA patients had an ultrasound (US) scan of their hand as per standardized protocols. US scores were expressed per joint and as a total US activity' score, (sum of power Doppler (PD) and grey-scale synovial hypertrophy scores in all joints) and a total erosion score. SLE disease activity was assessed (BILAG and SELENA-SLEDAI). Plasma levels of IL-6, TNF-alpha and BLyS were measured using sandwich ELISA kits (Quantikine kits, R & D). Results On the basis of the US results SLE patients were divided into three groups: erosive arthritis (n=20), non-erosive arthritis (n=18) and those with a normal US scan (n=12). Across the SLE groups plasma IL-6 levels correlated with CRP (p<0.001), hand deformity scores (p=0.005), BILAG musculoskeletal score (p=0.009), wrist PD score (p=0.01), the presence of tenosynovitis (p=0.008) and total US activity score (p<0.001) (which remained constant when corrected for total BILAG score). Neither TNF-alpha nor BLyS levels correlated with US or clinical measures of lupus arthritis; however, TNF-alpha correlated with total BILAG score (p<0.001). Conclusion This is the first study to examine levels of specific cytokines in a cohort of SLE patients stratified in terms of joint disease by US, where the most significant finding is that IL-6 levels correlated both with clinical and US measures of arthritis disease activity.