Assessment of bone involvement by DXA and HR-pQCT in patients with X-linked hypophosphatemia.

INTRODUCTION: X-linked hypophosphatemic rickets (XLH) is a rare disease and its natural history affects the quality of life of patients, as it leads to bone deformities and architectural and qualitative changes in the bone. MATERIALS AND METHODS: Sixteen XLH patients were selected from referral hospitals in Rio de Janeiro (12 women and four men) and compared to 16 healthy age- and sex-matched control individuals. All XLH were receiving calcitriol and oral phosphate supplements. Bone assessment was performed by high-resolution peripheral quantitative computed tomography (HR-pQCT) and dual-energy X-ray absorptiometry (DXA). RESULTS: XLH patients showed higher lumbar spine BMD Z-score, but lower 33% distal radius BMD and Z-score values as compared to control group. Low BMD for age (Z-score ≤ -2.0 SD) was only detected in the XLH group: specifically in 3 of the 5 postmenopausal women, 3 of the 7 premenopausal women, and 2 of the 4 men. HR-pQCT evaluation showed lower total vBMD at both peripheral sites and impaired trabecular parameters, particularly at the distal tibia, after correction for multiple comparisons. CONCLUSION: Our study sheds light on the involvement of both trabecular and cortical compartments in the XLH group, despite conventional treatment. We also emphasize the limitation of DXA in assessing central sites in the XLH group. The 33% radius may represent a useful complementary skeletal site for DXA assessment, particularly when HR-pQCT is not available.