Osteoporosis in patients with ankylosing spondylitis

Objective To study the frequency of osteoporosis,risk factors,relationship between bone turnover makers and bone mineral density (BMD) in patients with ankylosing spondylitis (AS).Methods BMD in the spine and femoral neck was measured with dual energy x ray absorptiometry(DEXA) in 30 AS patients.Enzyme linked immunoassay was used to measure serum bone Gla containing protein(BGP),bone specific alkaline phosphatase(BAP) and urine deoxypyridinoline crosslinks(D Pyr).Results The patients lost already the bone mass in early stage of AS, and had lower volume of BMD in both hip and spine than healthy controls.But in the late stage,the BMD of the spines was higher than that of the control group due to the calcification of the surrounding tissues of the spine,even the BMD of femoral neck was still lower than that of healthy objects.Osteoporosis was observed in 6 patients,osteopenia in 10.Osteoporosis in AS was related to disease duration,ESR,CRP,and X ray grades.The reduction of BMD in premenopausal women with early AS was slighter than that in men.The BMD had no significant differences between HLA B27(+) patients and HLA B27( ) patients.BGP and BAP,which reflect bone formation,had no differences between AS patients and controls.D Pyr that reflects bone resorption had significantly increased compared with controls.Conclusion Osteoporosis in AS is common and may be related to disease duration,activity and severity.A significant increase of bone resorption is observed in AS with osteoporosis.