Comparing the structural effects of TNFi and tocilizumab on the periarticular bone by performing a comprehensive analysis of the periarticular bone changes in RA patients treated with either TNFi or tocilizumab in a longitudinal Setting, using high-resolution peripheral quantitative computed tomography (HR-pQCT), a very sensitive method for visualizing and quantifying bone microstructure in RA patients. Quantitatively assessing the changes of erosions volume, osteophytes size and the area of cortical fenestration in a group of TNFi-treated and a group of tocilizumab- treated RA patients.

Inhibition of tumor necrosis factor alpha (TNF-α) and of interleukin- 6 receptor (IL-6R) emerged as highly effective cytokine blocking strategies in the treatment of rheumatoid arthritis (RA) in the last years. Both, inhibition of TNF-α (TNFi) and of the interleukin-6 receptor by tocilizumab ameliorate the signs and symptoms, reverse the elevated acute phase response and inhibit the progression of bone erosion in RA patients (1). Despite striking similarities with respect to their efficacy and safety in the treatment of RA, TNFi and tocilizumab are two entirely distinct approaches for targeting chronic inflammatory diseases in humans. This concept is highlighted by the differential response to TNFi and tocilizumab in other chronic inflammatory diseases such as psoriasis, psoriatic arthritis and spondyloarthritis, with clinical efficacy of the former but not the latter treatment modality (2). On the other hand, tocilizumab has a direct effect on the acute phase response and iron metabolism, which is not found with TNFi. Therefore, subtle differences may exist between TNFi and tocilizumab, which are relevant for the long-term treatment of RA patients.

Inclusion Criteria:

• Females and males with RA erosions in the wrist and/or MCP joints
• Must be aged ≥ 18 years at time of consent
• Stable treatment with conventional DMARDs of at least 3 months

Exclusion Criteria:

• Patients exposed to abatacept or rituximab in the last 12 months
• Patients receiving glucocorticoids over 5 mg prednisolone per day
• Patients who are younger than 18 years
• Pregnant or lactating females
• Patients having received an HR-pQCT examination during the last 6 months before screening

Patients (ages over 18 years) with the diagnosis of RA will be screened for the presence of erosions by Routine procedure with HR-pQCT. In case of a positive scan showing the presence of erosion in the wrist or the MCP Joints and after the decision of the treatment (if either Tocilizumab or TNF-Inhibitor), patients will be enrolled into the study.