Generalised osteoporosis is often described in patients with rheumatoid arthritis (RA). The aim of this study was to evaluate disease related determinants of bone mineral density (BMD) in patients with RA.
Subjects were selected from a group of 147 patients with recent onset RA. Disease activity and functional capacity were studied prospectively in this cohort. Activity of the disease was assessed once every three months by various parameters, and functional capacity was measured with a health assessment questionnaire once every six months. Ninety seven patients consented to participate in the study. Bone mineral density was assessed with dual energy x ray absorptiometry in the lumbar spine, in a combined region of interest in the hips, and in Ward's triangle. Multiple linear regression procedures were used to analyse the data.
Duration of RA was negatively associated with BMD at all three sites of measurement. The mean erythrocyte sedimentation rate in the six months before BMD measurement was negatively associated with BMD in the hip and in Ward's triangle. Other parameters of disease activity were not related to BMD. The mean health assessment questionnaire score in the 18 months before BMD measurement was negatively associated with BMD in the combined hip region only. Bone mineral density tended to be decreased when patients were compared with a normal reference group, especially in the femoral regions of interest.
It is concluded that BMD may be affected in patients with recent onset RA by disease dependent mechanisms. Several factors have been suggested elsewhere as determinants of BMD in RA. The results of this study show that disease duration, disease activity, and functional impairment may, independently of each other, contribute to bone loss, especially in the proximal femur.