Cytokine Biomarkers of Disease Activity and Therapeutic Response after Initiating Methotrexate Therapy in Patients with Juvenile Idiopathic Arthritis

tudy Objective To evaluate the relationship between plasma cytokine levels with disease activity and therapeutic response in patients with juvenile idiopathic arthritis after initiating methotrexate (MTX) therapy. Design Single-center, observational, prospective cohort study. Setting Outpatient pediatric rheumatology clinic at a tertiary care academic pediatric hospital. Patients Sixty-one patients diagnosed with juvenile idiopathic arthritis who started therapy with standard-dose methotrexate (MTX) 15 mg/m2/week; at 3 months, treating physicians were given the option of maintaining the MTX dose, increasing the MTX dose, or adding etanercept, based on their clinical judgment. Measurements and Main Results Patients were evaluated at baseline, 3 months (51 patients), and 6 months (35 patients). Plasma samples from each visit were analyzed for interleukin (IL)-1α, IL-1β, IL-1Ra, IL-6, and tumor necrosis factor-α (TNF-α). Cytokine concentrations were evaluated for relationships with disease activity using the 71–joint count Juvenile Arthritis Disease Activity Score (JADAS). Therapeutic response was assessed by changes in JADAS. Failure to respond to standard-dose MTX was defined as the need for the addition of etanercept or a MTX dose increase at or before the 3-month visit. Increased disease severity at baseline was associated with increased IL-6 (p=0.01) and TNF-α (p=0.008) levels. Initiation of MTX was associated with reductions in IL-1α (p=0.009), IL-1β (p=0.01), IL-1Ra (p=0.007), and IL-6 (p=0.03) levels; however, reductions in JADAS were only associated with reductions in IL-6 (p=0.009) and TNF-α levels (p=0.02). Compared with responders, patients failing to respond to standard-dose MTX had increased TNF-α levels at baseline (p=0.02) and 3 months (p=0.005). Reductions in JADAS by 6 months were observed following either the addition of etanercept (p=0.009) or an increase in MTX dose (p=0.007), but the addition of etanercept was associated with a median 7-fold increase in TNF-α levels (p=0.003) that corresponded with clinical response. Conclusion Plasma cytokine levels were responsive to MTX therapy in patients with juvenile idiopathic arthritis, but only TNF-α and IL-6 levels were consistently associated with disease activity and therapeutic response. Increased TNF-α levels at baseline were associated with failure to respond to standard-dose MTX and the need for more aggressive drug therapy. Initiation of etanercept resulted in increased TNF-α levels that corresponded with therapeutic response, which suggests a potential clinical benefit of monitoring TNF-α levels as a pharmacodynamic marker of etanercept activity. This article is protected by copyright. All rights reserved.