Whole body and regional bone mineral density in ankylosing spondylitis

Objective. To study the regional distribution of bone mass and look for fac tors leading to bone loss in ankylosing spondylitis (AS). Methods. Thirty-nine patients, all men, aged 20 to 55 years and presenting with AS were studied. Four hundred sixteen gendarmes, all men aged 20 to 55 years, formed an age matched control population used to define standard va lues for bone mineral density (BMD) in men. The patients with AS and the co ntrols underwent measurement of whole body BMD and regional BMD by dual-ene rgy x-ray absorptiometry. Results. AS was associated with spinal bone loss, with lumbar spine BMD (LS BMD) 1.085 +/- 0.178 g/cm(2) in the AS group compared with 1.232 +/- 0.136 g/cm(2) in the control group (p < 0.01). Whole body BMD and regional BMD of head, whole spine, pelvis, and legs were reduced, although this was not st atistically significant. Using standard values for LSBMD from the controls, we found that 46% (18/39) of patients with AS had Z score < -1.5 SD. Biolo gical markers of disease activity were higher in the subgroup of patients w ith low LSBMD than in the subgroup with normal LSBMD, with an erythrocyte s edimentation rate of 29.4 +/- 23.4 mm/h versus 12.1 +/- 10.8 mm/h (p < 0.05 ) and C-reactive protein at 24.8 +/- 18 mg/l versus 12.7 +/- 14.2 mg/l (p < 0.05). Conclusion. AS is associated with bone loss, mainly concerning the lumbar s pine,in patients whose disease is biologically most active.