Background Low bone mass at metacarpal (MC) diaphysis measured by radiogrammetry (DXR) has been described as a poor prognostic factor in rheumatoid arthritis (RA). However, this technique is not available in our environment. Our group has previously described the measurement of bone mineral density (BMD) at metacarpophalangeal joints (MCP) by dual X-ray absorptiometry (DXA). This measurement showed an acceptable correlation with the DXR at MC bones. However, DXR at MC bones mainly assesses cortical bone, whereas DXA at MCP mainly analyzes trabecular bone. Therefore, we have developed a procedure to evaluate MC's (2nd to 4th) bone mass of the nondominant hand through DXA.
Objectives To study the correlation between BMD at 2nd to 4th MC of the nondominant hand measured by DXA with data obtained by DXR.
Methods We studied 171 patients belonging to the Princesa Early Arthritis Register Longitudinal (PEARL) Study (84% women, 55.4 years at symptoms onset; 56.7% fulfilled RA 2010 criteria; 52% RF+ and 43.5% ACPA+). Demographic, clinical and laboratory data were collected per protocol. Hand X-rays were performed at baseline and after one year of follow-up, as well as nondominant hand BMD assessment by DXA (Hologic© QDR4500, Elite).
The standard Hologic© software allows to design regions of interest (ROI) tailored to the researcher needs. In order to develop ROIs in DXA similar to that in DXR, the ROI generator was placed on every MC mid third of the diaphysis (aprox 17x17 mm). The ROI was rotated to be aligned to the MC longitudinal axis, avoiding overlap between adjacent ROIs.
The BMD by DXA was the average of 3 successive measurements. The BMD by DXR was measured with standardized software Sectra (Linköping, Sweden) on hand digital X-ray (GE© DX Definium 8000).
Statistical analysis was performed using Stata 12 for Windows, including linear correlations according to the Spearman test between the BMD values of MC by DXA and DXR and BMD by DXA at global hand and MCP joints. In addition, a multivariate analysis was performed to determine which variables accounted for the differences between MC bone mass measured by DXR and DXA.
Results 248 BMD measurements (154 at baseline and 94 at second visit) of the 3 regions described whose values are shown in Table 1.
Conclusions As shown in table 1, MC bone mass measured by DXA shows the lowest absolute difference and the best correlation with MC bone mass by DXR. Female gender (beta coefficient =0.013; p=0.039), patients older than 65 years (beta coefficient =0.014; p=0.019) and patients with higher body mass index (beta coefficient =0.002 by kg/m2; p=0.019) were significantly associated with lower differences between the values of MC by DXA and DXR.
Acknowledgement FIS PI12/01578 y PI14/00442, Fondo Europeo de Desarrollo Regional (FEDER) and PFIZER Spain.
Disclosure of Interest I. Llorente Grant/research support from: Pfizer Spain, L. Merino: None declared, A. M. Ortiz: None declared, S. González: None declared, E. Escolano: None declared, J. A. García Vadillo: None declared, E. F. Vicente: None declared, R. García Vicuña: None declared, I. González Grant/research support from: Pfizer Spain, S. Castañeda Grant/research support from: Pfizer Spain