Serum IL-6 level as a marker of disease activity in ankylosing spondylitis patients with pure axial involvement

Abstract

BackgroundThe assessment of disease activity in patients with ankylosing spondylitis (AS) continues to be a challenging issue. The currently available markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) show poor correlation with clinical disease activity. ObjectivesTo compare serum IL-6 and hs-CRP levels between patients with AS with pure axial involvement and healthy controls; and to correlate them with Bath ankylosing spondylitis disease activity index (BASDAI), Bath ankylosing spondylitis functional index (BASFI) and Bath ankylosing spondylitis metrology index (BASMI). MethodsSixty-two consecutive patients of AS with pure axial involvement satisfying the modified New York criteria and 60 age-matched healthy controls were recruited. In all patients, Bath indices were measured and fasting venous blood samples for serum IL-6 and hs-CRP levels were obtained. Comparison of median of serum IL-6 and hs-CRP levels was done between cases and healthy controls and levels also correlated with Bath indices by appropriate statistical methods. ResultsThe median serum IL-6 and hs-CRP levels were significantly higher in cases as compared to healthy controls (p = 0.001). Serum IL-6 levels correlated significantly with BASDAI and BASFI (r = 0.61, p = 0.001 and r = 0.27, p = 0.032 respectively) but no correlation was found with BASMI (r = −0.08, p = 0.53). Serum hs-CRP did not correlate with Bath indices except BASMI (r = 0.28, p = 0.03). ConclusionSerum IL-6 levels can be reliably used as an aid in monitoring of disease activity in AS patients with pure axial involvement.