Effect of Paget's disease of bone on areal lumbar spine bone mineral density measured by DXA, and density of cortical and trabecular bone measured byquantitative CT

Although bone density may be increased in bone that is affected by Paget's disease, density changes in cortical and trabecular bone and the effect on bone that is apparently unaffected by Paget's disease are relatively unexpl ored. We have investigated 81 vertebrae (28 affected, 53 unaffected) in 27 patients with Pager's disease, by dual X-ray absorptiometry (DXA) and by qu antitative CT (QCT) bone density measurements of trabecular and cortical bo ne. DXA bone density was high (mean z-score=1.62, p<0.001) in vertebrae aff ected by Paget's disease, but not significantly different from normal in un affected vertebrae (mean =-score=0.07, ns). Mean QCT I-score in Paget's ver tebrae was 2.07 (p=0.009) for cortical bone and 1.37 (p=0.008) for trabecul ar bone. DXA correlated with QCT cortical values in affected and unaffected bone (r=0.8 and 0.56. respectively), and with QCT trabecular values (r =0. 72 and 0.48, respectively). There was no significant difference in the slop es for the correlations in affected or unaffected bone. Cortical QCT values are underestimated in Paget's disease compared with physical measurements of density, owing to the computer algorithm used. High DXA values may alert to the possibility of Paget's disease, especially if the value deviates fr om the expected normal sequence in lumbar vertebrae. Osteoporotic vertebrae may be overlooked if the average value of bone mineral density is taken in the lumbar spine without reviewing each vertebra.