The effects of tocilizumab on osteitis, synovitis and erosion progression in rheumatoid arthritis: results from the ACT-RAY MRI substudy.

Objective: To examine the imaging-detected mechanism of reduction of structural joint damage progression by tocilizumab (TCZ) in patients with rheumatoid arthritis (RA) using MRI.

Methods: In a substudy of a randomised, double-blind, phase 3b study (ACT-RAY) of biologic-naïve patients with RA who were methotrexate (MTX)-inadequate responders, 63 patients were randomised to continue MTX or receive placebo (PBO), both in combination with TCZ 8 mg/kg every 4 weeks, with optional additional disease-modifying antirheumatic drugs at week 24 if Disease Activity Score of 28 joints < 3.2. The most symptomatic hand was imaged with 0.2 Tesla extremity MRI at weeks 0, 2, 12 and 52. MR images were scored using Outcome Measures in Rheumatology-Rheumatoid Arthritis Magnetic Resonance Imaging Score. Predictors of week 52 erosion progression were determined by logistic regression analysis.

Results: TCZ + PBO (n=32) demonstrated mean improvements in synovitis from baseline to weeks 2 (-0.92; p=0.0011), 12 (-1.86; p<0.0001) and 52 (-3.35; p<0.0001), while TCZ + MTX (n=31) had mean improvements in synovitis at week 12 (-0.88; p=0.0074), but not week 52 (-1.00; p=0.0711). TCZ+PBO demonstrated mean reductions in osteitis at weeks 12 (-5.10; p=0.0022) and 52 (-8.56; p=0.0006), while TCZ+MTX had mean reductions at weeks 2 (-0.21; p<0.05) and 12 (-3.63; p=0.0008), but not week 52 (-2.31; p=0.9749). Mean erosion scores did not worsen in either group. MRI erosion scores at weeks 12 and 52 correlated strongly with radiography erosion scores at week 52 (r>0.80). Baseline synovitis and worsening of osteitis predicted erosion progression.

Conclusions: Rapid suppression of synovitis and osteitis with reduction in structural joint damage progression occurred with TCZ, as monotherapy or in combination with MTX, through week 52.