POS0595 THE ASSOCIATION BETWEEN AXIAL AND PERIPHERAL BONE IN PATIENTS WITH RHEUMATOID ARTHRITIS, INCLUDING THE IMPACT OF EROSIVE DISEASE. A HR-pQCT STUDY.

Abstract

BackgroundThe severity of Rheumatoid Arthritis (RA) is associated with increased fracture risk (1). Areal bone mineral density (aBMD) by dual-energy absorptiometry (DXA) is the gold standard for diagnosis of osteoporosis as well as fracture risk assessment. High resolution peripheral quantitative computed tomography (HR-pQCT) of the distal radius yields volumetric BMD (vBMD) of trabecular and cortical bone compartments, as well as micro-architectural parameters and may prove useful for fracture risk prediction. The association between aBMD by DXA and HR-pQCT derived vBMD and microarchitecture have only been sparsely investigated in patients with RA, and it is not known if erosive disease, measured by the gold standard Heijde-modified Sharp Scores (HSS) (2) affects HR-pQCT derived parameters.ObjectivesTo assess the associations between aBMD by DXA and bone parameters of the distal radius by HR-pQCT, in both male and female patients with RA, and the impact of erosive disease on the bone parameters of the distal radius.MethodsWe measured aBMD by DXA of the lumbar spine and hip, HR-pQCT of the distal radius and assessed HSS in 162 patients with RA. Using multivariate linear regression models, we explored the association between HSS and HR-pQCT parameters, adjusted for sex and age. The associations between aBMD by DXA and vBMD and microarchitecture by HR-pQCT were assessed by Spearman correlation coefficients, interpreted as negligeable (0.00-0.10), weak (0.10-0.39), moderate (0.40-0.69), strong (0.70-0.89) or very strong (0.90-1.00).ResultsMean age for the included patients was 63 years, 75% were women and median disease duration was 18 years. Erosive disease (HSS) was negatively associated with trabecular number and density, but not with cortical bone parameters. This association was stronger for HSS of the wrist joints, than for HSS of the hands and total HSS (Table 1). Trabecular density of the distal radius correlated moderately with aBMD at the total hip, and weakly with aBMD at the lumbar spine. Trabecular numbers also correlated moderately with aBMD at the total hip. Cortical bone parameters at the distal radius correlated weakly with aBMD at the hip, but only among women.Table 1.Multivariate linear regression model exploring the effect of Heijde-modified Sharp Score on selected HR-pQCT (distal radius) parameters, adjusted for age and sex.R2Effectp-valueHSS total (n=146)Tt. BMD (mg HA/cm3)0.129-0.0520.519Ct. BMD (mg HA/cm3)0.1380.0600.642Ct. Th (mm)0.0960.0010.084Tb. BMD (mg HA/cm3)0.284-0.173<0.001Tb. N (1/mm)0.319-0.003<0.001HSS of the hands (n=145)Tt. BMD (mg HA/cm3)0.124-0.0730.522Ct. BMD (mg HA/cm3)0.1320.0460.801Ct. Th (mm)0.0870.0010.122Tb. BMD (mg HA/cm3)0.279-0.2420.001Tb. N (1/mm)0.324-0.005<0.001HSS of the wrists (n=146)Tt. BMD (mg HA/cm3)0.127-0.1210.614Ct. BMD (mg HA/cm3)0.136-0.0290.939Ct. Th (mm)0.0890.0010.158Tb. BMD (mg HA/cm3)0.273-0.4670.003Tb. N (1/mm)0.311-0.010<0.001HR-pQCT: high resolution peripheral quantitative computed tomography,HSS: Heijde-modified Sharp Score, Tt.: total, Ct.: cortical, Tb.: trabecular, BMD: bone mineral density, HA: hydroxyappatite, Th.: Thickness, N: numberConclusionAmong patients with RA, the correlation between axial and peripheral bone is strongest between trabecular bone parameters of the radius and aBMD at the hip, which suggests that prediction of hip fractures is maintained. However, the degree of erosive disease negatively impacts the trabecular bone parameters. This may potentially interfere with the hip fracture prediction abilities of HR-pQCT in patients with high degree of erosive disease.