Preliminary results obtained in 15 patients (7 females and 8 males, mean age: 27.7 years) demonstrated that only some HR-pQCT parameters correlate well with DXA-aBMD, as shown in Table 1 (radius) and 2 (tibia).
The strongest and most significant correlations were found between DXA-aBMD at the ultradistal radius and total vBMD (r = 0.89), cortical vBMD (r = 0.83), and Ct.Th (r = 0.87) at the distal radius. This agreement in terms of BMD measurement by DXA and HR-pQCT could be explained by the close proximity of the areas of interest at the ultradistal radius. One study conducted in post-menopausal women also demonstrated good agreement between DXA-aBMD and vBMD by HR-pQCT measured at the ultradistal radius [15]. Of note, in our population, the relationship between total vBMD at the radius and DXA-aBMD at the ultradistal radius was mostly explained by good agreement with cortical vBMD, because trabecular vBMD was not significantly correlated with aBMD at the ultradistal radius.
In addition, Ct.vBMD correlated with aBMD at the 1/3 radius as well.
Poor correlation was found between DXA-aBMD measured at central sites (lumbar spine and hip) and vBMD measured at peripheral sites with HR-pQCT, which could suggest that bone composition at central sites does not reflect well that at distal sites in OI.
Whole-body DXA-aBMD correlated significantly with Tt.vBMD, Ct.vBMD, Ct.Th, and Ct.Ar at both the radius and tibia. However, it should be considered that whole-body DXA is not indicated in adults for the diagnosis of low bone mass [12] and that only 12 out of the total 15 patients included in our analysis underwent whole-body DXA.
It is interesting to note that Ct.Ar measured by HR-pQCT at both the radius and tibia was correlated with DXA-aBMD at all sites. Although the significance of this relationship is still unclear, Ct.Ar was found to be one of the best HR-pQCT parameters differentiating patients with OI type I from healthy controls in one study [8].
On the other hand, there were no significant correlations between DXA-aBMD and trabecular HR-pQCT parameters (vBMD, number, thickness, separation) at the distal radius, and only few moderate or weak correlations at the distal tibia. In particular, only total femur aBMD was correlated with Tb.vBMD (r = 0.58) at the tibia, while both total femur and femoral neck aBMD were correlated with BV/TV (r = 0.63 and 0.53, respectively) at the tibia. The lack of agreement between DXA-aBMD and trabecular HR-pQCT parameters is notable, especially given that some studies suggested that trabecular HR-pQCT parameters could be the most deteriorated in patients with OI in comparison with healthy controls [8, 9].