Site-specific variation in the classification of osteoporosis, and the diagnostic reclassification using the lowest individual lumbar vertebra T-score compared with the L1-L4 mean, in early postmenopausal women

In this study we report first the concordance and variation in diagnostic o steoporosis classification using multiple skeletal site measurements compar ed with the lumbar spine only; and secondly, at the lumbar spine, the varia tion and diagnostic osteoporosis reclassification using the lowest individu al vertebra T-score compared with the L1-L4 mean T-score. One hundred and f ifty early postmenopausal women were evaluated as part of the recruitment f or a multicenter osteoporosis prevention study. Bone mineral density (BMD) was restricted such that no more than 10% of the subjects had a lumbar spin e BMD below 0.8 g/cm(2). Forty-seven per cent of the subjects were classifi ed as having low bone mass (T-score less than or equal to -1.0) at the lumb ar spine, 63% at the mid-forearm, 39% at the distal forearm and 50% at the hip (p<0.05). The greatest proportion of subjects were categorized as osteo porotic at the lumbar spine, followed by the forearm and then the hip. Corr elation between sites ranged from 0.57 to 0.60 (p<0.01). Eighty-one percent of the subjects had a significant difference between their highest and low est individual lumbar vertebra T-score (defined as difference outside the 9 0% confidence interval coefficient of variation T-score value). Using the l owest individual lumbar T-score, recategorized 33% of the subjects classifi ed as osteopenic (based on the mean L1-L4 T-score) as osteoporotic, and 23% of those classified as normal as osteopenic (p<0.05). Of all four vertebra e, L2 had the highest T-score in 37.7% of the subjects (mean -0.3) and L4 t he lowest in 61% (mean - 1.5) (mean difference 1.2 units, 95% CI 0.7 to 1.7 ). The classification of osteoporosis varies according to skeletal site, wi th pronounced differences in the early menopausal population. T-scores are useful for characterizing subjects with the highest risk of osteoporosis bu t BMD and fracture risk must be recognized in a continuum. Individual T-sco res of the lumbar vertebrae show wide variation in the absence of degenerat ive spinal disease or vertebral collapse and the use of the lowest, signifi cantly different, individual lumbar vertebra T-score reclassified over half of the subjects in this study. This poses a great therapeutic dilemma in c linical practice. particularly if these fractures are at higher risk of fut ure collapse.