Bone density, ultrasound measurements and body composition in early ankylosing spondylitis

Abstract

Objectives. In this cross-sectional study, we evaluated bone density using both dual-energy X-ray absorptiometry (DEXA) and quantitative ultrasound (QUS) techniques and examined the changes in body composition in patients with ankylosing spondylitis (AS). Methods. Seventy-one patients were compared with seventy-one sex- and age-matched controls. Bone mineral density (BMD) was evaluated at the lumbar spine and femoral neck with a Lunar device. Total body measurements were also performed, giving BMD and bone mineral content (BMC) of the whole body, and fat and lean masses. Broadband ultrasound attenuation (BUA), speed of sound and stiffness were measured at the calcaneus using an Achilles ultrasound device. Results. The patients had significantly lower lumbar spine, femoral neck and total body BMD as compared with controls (all P < 0.05). Total body BMC was also decreased in AS (P = 0.002). On the contrary, fat and lean masses did not differ between patients and controls as observed for QUS values. Mild to good correlations were found between BMD and QUS parameters (r ranging from 0.22 to 0.53; all P ≤ 0.01). When applying the World Health Organization (WHO) definition for osteoporosis, we found that 46.5% of patients had lumbar spine osteopenia and/or osteoporosis, while 26.8% had femoral neck osteopenia and/or osteoporosis (controls: 23.9 and 10%; P = 0.001 and 0.08, respectively). No relationships between disease activity (as evaluated by erythrocyte sedimentation rate, serum C-reactive protein levels and BASDAI, a clinical index of disease activity) and BMD measurements were found and only femoral neck BMD correlated with disease duration (r = -0.25; P = 0.04). Finally, the presence of talalgia in AS did not influence the QUS values. Conclusion. These results confirm that AS patients have decreased BMD values at both the spine and femur, and also in total body measurements, reflecting a generalized bone loss. On the contrary, soft tissue composition does not seem to be influenced by the disease. QUS parameters were found to be similar between patients and controls, suggesting that the QUS method did not provide additive information to DEXA. As it is thought that QUS provides information about qualitative properties of bone, the normal results of QUS values in our patient series argue against modifications in AS bone micro-architecture.