Bone mineral density, calcaneal ultrasound, and bone turnover markers in women with ankylosing spondylitis.

OBJECTIVE

To assess bone mineral density (BMD) by dual energy x-ray absorptiometry (DEXA) and calcaneal quantitative ultrasound (QUS) in a cohort of pre- and postmenopausal women with ankylosing spondylitis (AS), and to determine any relationships with markers of bone turnover and disease activity or severity.

METHODS

Fifty premenopausal and 16 postmenopausal women with AS were studied. Clinical and radiological status was assessed by the Bath AS Disease Activity Index (BASDAI), Bath AS Functional Index (BASFI), Bath AS Metrology Index (BASMI), and Bath AS Radiology Index (BASRI). BMD of the hip and spine was measured by DEXA, and QUS measured at the heel. Serum osteocalcin (OC), bone-specific alkaline phosphatase (BALP), urinary D-pyridinoline crosslinks (D-PYR), and C-reactive protein (CRP) were assayed.

RESULTS

Women with AS (n = 66) had reduced BMD at the hip compared to age and sex matched controls (n = 132). The mean t scores were -1.1 and -2.0, and z scores -0.4 and -0.37, for pre- and postmenopausal women, respectively. Four (6%) had osteoporosis and 34 (52%) had osteopenia according to the WHO definitions. Using a multiple regression model, femoral neck BMD was found to be significantly affected by age, body mass index, and the sacroiliac radiographic score. There were no significant correlations of BMD with disease duration or disease activity. QUS measures did not correlate with DEXA measures of BMD. Women with AS had significantly lower markers of bone formation, OC and BALP, and a trend to higher D-PYR than controls. Serum OC levels correlated negatively with femoral neck BMD, whereas D-PYR correlated with CRP levels.

CONCLUSION

Women with AS have reduced hip BMD, 0.39 SD below age and sex matched controls. Bone turnover in women with AS is characterized by low OC and BALP.