Association between serine proteinase activity and response to intra-articular corticosteroid injections in psoriatic arthritis
Objective: Intra-articular corticosteroid (IAS) injections are often used for the immediate relief of pain and inflammation in the joint of psoriatic arthritis (PsA) patients. However, studies identifying factors that can predict response to IAS injections are lacking. We aimed to assess the usefulness of serine proteinase activity measurements in PsA synovial fluid (SF) samples obtained at the time of injection in predicting clinical response. Methods: PsA patients with available SF samples from the knee joint were identified from the University of Toronto PsA cohort. Clinical response was defined as an absence of tenderness or swelling in the injected joint at the first post-injection visit, at either 3 or 6 months. Proteinase activity was determined by measuring cleavage of fluorogenic tri-peptide substrates for trypsin-like (VPR-AMC and VLK-AMC) and chymotrypsin-like (AAPF-AMC) serine proteinases. Generalized estimating equation (GEE) models were used to investigate which factors were associated with response. Results: A total of 32 patients with 60 injected joints and data available for follow-up at 3 or 6 months were included in the analysis, with 25 (41.7%) injected joints resulting in clinical response. Age, sex, active joint count, medications and serine proteinase activity at the time of injection were included as covariates. Only treatment with biologics was significantly associated with response at 3 or 6 months in the multivariate reduced model (OR 3.02, p = 0.027). Conclusion: We could not demonstrate an association between SF serine proteinase activity and response to IAS injection. Biologic agents significantly improve the likelihood of achieving clinical response.