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SAT0515 Seropositive Rheumatoid Arthritis has a Distinctive Bone Phenotype at the Ultra-Distal Radius Compared to Seronegative Rheumatoid Arthritis and Psoriatic Arthritis

Background Psoriatic arthritis (PsA) and rheumatoid arthritis (RA) are chronic inflammatory joint diseases characterized by periarticular and systemic bone loss. As a consequence, fracture risk is increased in both disorders. However, pathogenesis and radiological characteristics are different and areal bone mineral density, measured by dual-energy x-ray absorptiometry (DXA) does not reflect bone status adequately in PsA and RA. Objectives The aim of this study was to compare bone quality, including volumetric bone density (vBMD) and microstructure of trabecular and cortical bone, assessed by high-resolution peripheral quantitative computed tomography (Xtreme-CT) in patients with PsA and RA at the distal radius. Methods We investigated 50 patients with PsA (24 female, 26 male, mean age 50.5 ± 13.1 years, PsA) and 60 patients with RA (33 female, 27 male, mean age 53.7 ± 12.3 years, RA). RA was divided into seropositive RA (Anti-cyclic citrullinated peptide antibody (anti-CCP) and/or rheumatoid factor (RF) positive, RA+, n=38) and seronegative RA (RA-, n=22). HR-pQCT measurements (Xtreme-CT, Scanco Medical AG, Brüttisellen, Switzerland) were carried out at the ultra-distal radius using the manufacturer’s standard protocol. Scanning was performed within a region of 110 slices proximal to the reference line. Data were compared between RA+, RA- and PsA. In addition, correlations between demographic data, vBMD and microstructure were carried out in all subgroups. Results Patients with RA did not differ from patients with PsA regarding age, BMI, duration of disease, DAS28, CRP or HAQ. Erosions were detected in 72% (RA) and 70% (PsA) of patients, respectively. No significant differences were found for vBMD or structure parameters between RA and PsA and RA- and PsA. However, RA+ showed significantly decreased values for total trabecular bone density (Dtrab, p=0.007), the peripheral trabecular density adjacent to the cortex (Dmeta, p=0.002) and the central medullary trabecular density (Dinn, p=0.021) compared to PsA. Moreover, trabecular bone volume fraction (BV/TV, p=0.007) and trabecular number (Tb.N, p=0.044) were significantly lower in RA+. In addition, trabecular separation (Tb.Sp, p=0.046) was significantly increased in RA+ compared to PsA. Significantly lower trabecular density parameters (Dtrab, p=0.007; Dmeta, p=0.007; Dinn, p=0.014) and microstructure including BV/TV (p=0.007) and Tb.N (p=0.08) as well as increased Tb.Sp (p=0.016) were also found for RA+ in comparison to RA-. Conclusions Our data strongly suggest a distinct bone phenotype in RA+ compared to RA- and PsA. RA+ shows significantly lower trabecular vBMD and low quality microstructure of the bone, independently from age. Autoantibody status thus seems to play a dominant role, not only in local, but also in systemic bone loss. Disclosure of Interest R. Kocijan Grant/research support from: Bayerische Forschungsstiftung, S. Finzel: None Declared, M. Englbrecht: None Declared, A. Kleyer: None Declared, J. Rech: None Declared, G. Schett: None Declared