Comparison of the effects of tocilizumab monotherapy and adalimumab in combination with methotrexate on bone erosion repair in rheumatoid arthritis

Objective To compare the effects of interleukin-6 (IL-6) receptor and tumour necrosis factor inhibition on inducing repair of existing bone erosions in patients with very early rheumatoid arthritis (RA). Methods Prospective non-randomised observational study in patients with active erosive RA with inadequate response to methotrexate (MTX) receiving either tocilizumab (TOC) monotherapy or adalimumab (ADA) with MTX for 52 weeks. Erosion volumes were assessed in metacarpal heads (MCH) and the radius by high-resolution peripheral quantitative CT at baseline and after 52 weeks. Clinical response was monitored using Clinical Disease Activity Index, Simple Disease Activity Index and Disease Activity Score 28-erythrocyte sedimentation rate (DAS28-ESR) scores every 12 weeks. Results TOC (N=33) and ADA/MTX (N=33) treatment groups were balanced for age, sex, body mass index, comorbidities, disease and activity, functional state, autoantibody status, baseline bone damage and baseline bone biomarkers. Both TOC (DAS28-ESR: baseline: 6.2 +/- 0.5; 52 weeks: 2.3 +/- 1.0) and ADA/MTX (6.3 +/- 0.6; 2.8 +/- 1.2) significantly reduced disease activity. Erosion volumes significantly decreased in the MCH and radius of patients with RA treated with TOC (p<0.001) but not in patients treated with ADA/MTX (p=0.77), where they remained stable in size. Mean decrease in erosion volume in TOC-treated patients was -1.0 +/- 1.1 mm(3) and -3.3 +/- 5.9 mm(3) in the MCH and radius of TOC-treated patients, respectively, and -0.05 +/- 0.9 mm(3) and -0.08 +/- 4.1 mm(3) in patients treated with ADA/MTX. Conclusions The REBONE study shows that TOC monotherapy achieves more pronounced repair of existing bone erosions than ADA/MTX. Hence, IL-6 is a central factor for the disturbed bone homeostasis in the joints of patients with RA.