Modification of structural lesions on MRI of the sacroiliac joints by etanercept in the EMBARK trial: a 12-week randomised placebo-controlled trial in patients with non-radiographic axial spondyloarthritis

Objective To evaluate the impact on structural lesions observed on MRI in the sacroiliac joints (SIJ) at 12 weeks in patients with non-radiographic axial spondyloarthritis (nr-axSpA) receiving etanercept or placebo in EMBARK (Effect of Etanercept on Symptoms and Objective Inflammation in nr-axSpA, a 104 week study). Methods Patients were randomised to double-blind etanercept 50 mg/week or placebo for 12 weeks. Structural lesions at baseline and 12 weeks were scored by two independent readers using the Spondyloarthritis Research Consortium of Canada (SPARCC) SIJ structural score (SSS) on T1-weighted MRI. Change in SPARCC SSS and correlation with improvement in clinical outcomes was evaluated. Results MRI scans from 185 patients (etanercept, n=88; placebo, n=97) were reviewed. At baseline, there were no significant differences in mean SPARCC SSS between etanercept and placebo. From baseline to 12 weeks, change in mean SPARCC SSS was significantly greater for etanercept than placebo for erosion (-0.57 vs -0.08, respectively, adjusted p value=0.017) and backfill (0.36 vs 0.06, adjusted p value=0.022). A treatment difference was also present for the subgroup of patients with SIJ inflammation on MRI (SPARCC bone marrow oedema >= 2): erosion: -0.81 versus -0.13 for etanercept versus placebo, respectively, p=0.007; backfill: 0.48 versus 0.08, respectively, p=0.032. Decrease in erosion and increase in backfill correlated with improvement in more clinical outcomes for etanercept than placebo. Conclusion Treatment with etanercept was associated with significantly greater reduction in erosions and increase in backfill at 12 weeks compared with placebo, consistent with a very early reparative response to antitumour necrosis factor therapy. The impact on disease progression in spondyloarthritis should be studied further.