Quantitative ultrasound in adults with cystic fibrosis: Correlation with bone mineral density and risk of vertebral fractures

In several conditions, including cystic fibrosis (CF) and corticosteroid-induced osteoporosis, bone mineral density (BMD) measurements provide a modest prediction of fracture risk. We investigated in adult CF patients whether quantitative ultrasound (QUS) parameters were able to discriminate between patients with and without prevalent vertebral fractures. One hundred seventy-two adults with CF, 91 men and 81 women, often on chronic oral or inhaled corticosteroid therapy, were studied. BMD at the lumbar spine, proximal femur, and total body were measured by dual-energy X-ray absorptiometry (DXA). QUS parameters were assessed by Achilles Express at the calcaneus and by the DBM Sonic 1200 at the phalanges. All bone measurements by DXA and QUS were significantly correlated with each other, with the exception of phalangeal amplitude-dependent speed of sound versus spine BMD. The mean T-score values in CF patients with and without prevalent vertebral fractures were similar for all DXA measurements and for stiffness index. A significant difference between the two groups was observed only for phalangeal ultrasound bone profile index (UBPI) values (relative risk = 1.25, 95% confidence interval 1.05-1.49 for each decrease in T score), and this difference was maintained after adjusting the values for age, body weight, forced expiratory volume in 1 second, gender, and corticosteroid use. In conclusion, only a phalangeal QUS parameter (UBPI), in contrast with calcaneus QUS or DXA measurements, was able to discriminate CF patients with from those without vertebral fractures, possibly as a result of qualitative alterations of bone tissue independent of BMD.