Objective. To determine which measurement of bone mineral density (BMD) predicts vertebral fractures in a cohort of postmenopausal women with glucocorticoid-induced osteoporosis. Methods. We recruited 114 subjects into the study. All had osteopenia of the lumbar spine or hip, as demonstrated by dual x-ray absorptiometry (DXA), and were receiving long-term glucocorticoids and hormone replacement therapy (HRT). Measurements of BMD by DXA of the lumbar spine, hip (and subregions), and forearm (and subregions), quantitative computed tomography (QCT) of the spine and hip (n = 59), and radiographs of the thoracolumbar spine were performed on all subjects to assess prevalent vertebral fractures. Vertebral fracture prevalence, as determined by morphometry, required a ≥20% (or ≥4-mm) loss of vertebral body height. Demographic information was obtained by questionnaire. Multiple regression and classification and regression trees (CART) analyses were used to assess predictors of vertebral fracture. Results. Twenty-six percent of the study subjects had prevalent fractures. BMD of the lumbar spine, total hip and hip subregions, as measured by QCT, but only the lumbar spine and total hip, as measured by DXA, were significantly associated with prevalent vertebral fractures. However, only lumbar spine BMD as measured by QCT was a significant predictor of vertebral fractures. CART analysis showed that a BMD value < 0.065 gm/cm3 was associated with a 7-fold higher risk of fracture than a BMD value ≥0.065 gm/cm3. Conclusion. In postmenopausal women with osteoporosis induced by long-term glucocorticoid treatment who are also receiving HRT, BMD of the lumbar spine as measured by QCT, but not DXA, is an independent predictor of vertebral fractures.
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