Titer-Dependent Effect of Anti-Citrullinated Protein Antibodies On Systemic Bone Mass in Rheumatoid Arthritis Patients

Abstract

Bone loss in rheumatoid arthritis (RA) is a key feature both local and systemic. Anti-citrullinated protein antibodies (ACPA) have recently been found to directly induce differentiation and activation of osteoclasts and therefore contribute to periarticular bone loss. The aim of this study was to analyze the effect of ACPA on systemic bone mineral density (BMD) in patients with established RA. This is a cross-sectional study with a single-center RA population. BMD was measured with Dual X-ray absorptiometry at lumbar and femoral sites. ACPA were measured by EIA. Multivariate analysis was performed adjusting for the main confounding variables. One hundred twenty-seven RA patients were enrolled. In univariate analysis, ACPA-positive patients showed lower BMD Z-score (SD below the age- and gender-matched mean reference value) at femoral sites (p < 0.01). A negative correlation between ACPA titer and BMD Z-score at all sites was observed (p < 0.01). The multivariate analysis adjusted for the main confounding variables confirmed the negative effect of ACPA at femoral sites (p < 0.05), but not at lumbar spine BMD. No significant effect of rheumatoid factor has been observed. ACPA have a negative titer-dependent effect on BMD at femoral sites, mainly constituted by cortical bone. ACPA-positive patients, especially if at high titer, should undergo bone investigations and be treated with bone protecting agents. Disease-modifying anti-rheumatic drugs lowering ACPA titer might have positive effects on systemic bone mass.

Keywords: ACPA; Bone mineral density; Osteoporosis; Rheumatoid arthritis.