ESPE Abstracts

Background: Previous studies evaluating bone quality and microarchitecture in X-linked hypophosphatemic rickets (XLH) have produced conflicting data.

Objective and hypotheses: To evaluate the bone mineral density (BMD) and microarchitecture in 36 XLH patients (13 children and 23 adults) with confirmed PHEX mutations compared to healthy controls.

Method: The areal BMD (aBMD) at lumbar spine (L1-L4), femoral neck, total hip and distal radius was evaluated by dual-energy x-ray absorptiometry (DXA). The volumetric BMD (vBMD) and the microarchitectural parameters were evaluated at the distal radius and tibia by high resolution peripheral quantitative computed tomography (HR-pQCT).

Results: XLH patients presented with a higher aBMD at L1-L4 (P<0.01), a lower aBMD at the distal third of the radius (P<0.01) and a trend towards lower aBMD at the total radius (P=0.12). There were no differences between groups at the femoral neck, total hip and ultradistal radius (P=0.49, P=0.90 and P=0.57, respectively). No differences were observed in vBMD at the radius (P=0.50), although the patients presented with a lower total vBMD (P<0.01) at the tibia compared to the controls, likely resulting from a decreased trabecular vBMD (P<0.01). Regarding the microarchitectural parameters, XLH patients presented a lower trabecular number (P<0.01), a greater trabecular separation (P<0.01) and a more inhomogeneous trabecular network (P<0.01) at both sites. In summary, HR-pQCT analysis showed microarchitectural changes in XLH patients at the radius and tibia; moreover, decreased trabecular vBMD was found mainly at the tibia. On the other hand, DXA analysis presented heterogeneous results at the different sites probably due to the influence of anatomical and anthropometric factors.

Conclusion: HR-pQCT was more informative than DXA in the bone evaluation of XLH patients. In contrast, DXA results should be interpreted carefully in this group of subjects.