Densitometry in glucocorticoid-induced osteoporosis

The technique of choice for the measurement of bone mineral density (BMD) in patients with glucocorticoid-induced osteoporosis (GIOP) is dual X-ray absorptiometry (DXA), which has been demonstrated to be reliable in diagnosing osteoporosis and monitoring bone mass variations over time in GIOP. However, in patients with both exogenous (i.e. due to glucocorticoid therapy) and endogenous cortisol excess, the BMD decrease does not fully explain the high risk of fractures. Therefore, the BMD thresholds in guidelines for the prevention of GC-related fractures are different and debated. Quantitative computed tomography (QCT), which is useful to separately study cortical and trabecular bone and to measure true "volumetric" BMD, has been suggested to be a better predictor of vertebral fractures than DXA. However, QCT has the limit of the possible underestimation of bone mass and QCT T-scores may be lower as compared to DXA T-score values for the same skeletal site. Quantitative ultrasound, which is considered to reflect both BMD and structural properties of bone such as connectivity and elasticity, is able to diagnose low BMD in GIOP, but its role in monitoring BMD changes and in predicting fracture's risk remains unknown. Low BMD and high rate of bone loss have been suggested to be possible complications even of subclinical hypercortisolism regardless for gender and gonadal status. On the other hand, low BMD and vertebral fractures may be the initial presentation of an otherwise asymptomatic cortisol excess.