Predictors of response to intra-articular steroid injection in psoriatic arthritis

Objectives. To assess the effectiveness of IA corticosteroid (IAS) injections in PsA and to determine the association between macrophage migration inhibition factor (MIF) gene polymorphism and response to IAS injections. Methods. A cohort analysis of PsA patients who were followed prospectively was performed. Clinical response was defined as no tenderness or effusion in the injected joint at 3 months. Relapse was defined as re-occurrence of joint pain or effusion. MIF 173C>G genotyping (rs755622) was performed. Results. Two hundred and twenty patients with 245 IAS injections were included in the study. The probability of responding at 3 months was 41.6%. Within 12 months, 25.5% of the joints relapsed. Clinical factors that were associated with response included duration of psoriasis [Odds ratio (OR) 1.03] and the use of MTX or anti-TNF agents at the time of injection (OR 2.68). Factors that were associated with relapse included injection into large joints (OR 4.58) and elevated sedimentation rate (OR 15.0), whereas absence of clinical and/or radiographic damage (OR 0.23) and duration of PsA (OR 0.92) reduced risk of relapse. MIF polymorphism was not associated with clinical response, but was associated with relapse (OR 3.2). On multivariate analysis including clinical covariates, the association between MIF polymorphism and relapse was lost. Conclusions. IAS injections are effective in PsA. MIF gene polymorphism is associated with relapse. However, this effect is explained by clinical variables that reflect disease activity, suggesting that MIF gene polymorphism influences inflammatory activity.