MO542: Bone Mineral Density, Bone Micro-Architecture Evolution After Kidney Transplantation: A Prospective Cohort Study
Authors: Bouquegneau Antoine , Malaise Olivier , Seidel Laurence , Bonvoisin Catherine , Weekers Laurent , Jouret François , Cavalier Etienne , Delanaye Pierre 
Published: May 2022

Abstract

BACKGROUND AND AIMS
Bone loss and mineral abnormalities are frequent in kidney transplant recipients (KTRs) and associated with a high risk of fracture, cardiovascular mortality and an increase in health care costs. In daily clinics, the detection of bone abnormalities after transplantation includes bone biomarkers and imaging technique [Dual Energy X-ray (DEXA)] to assess respectively the bone turnover and the bone mineral density (BMD), but with limitations. The high-resolution peripheral quantitative computed tomography (HR-pQCT) provides additional noninvasive information on bone microarchitecture and BMD with a better distinction between cortical and trabecular areas. The goal of our study is to evaluate the evolution of bone structure using HR-pQCT compared to standard technique (DXA) in a prospective cohort of KTRs.

METHOD
All patients referred for a single kidney transplant at the university hospital of Liège with no history of exposure to antiresorptive agents were eligible for inclusion (NCT04713774). Participants underwent baseline and 3-month biomarkers analysis, BMD measurements by DEXA. HR-pQCT images were obtained of the distal radius and distal tibia (non-dominant, non-fractured limb) using the XtremeCT device with standard protocols. HR-pQCT assessed quantitative measurement of the volumetric density of trabecular and cortical bone as well as bone structure (trabecular number or thickness or cortical porosity for instance).

RESULTS
A total of 26 patients were prospectively included. The mean age was 57.3 ± 12.1 years. The mean dialysis vintage was 27.5 ± 16.4 months before transplantation. Bone biomarkers showed a significant decrease at 3 months after transplantation. PTH decreased from 221.72 ng/L to 59.6 ng/L (P &lt; 0.0001), P1NP from 211 ug/L to 72 ug/L (P &lt; 0.013) and BLAP from 23 ug/L to 13 ug/L (P = 0.042). BMD was measured by DXA and HR-pQCT at 7 days [6; 8] and 102 days (90; 113) after transplantation. We observed a significant reduction of BMD by DXA at the hip site from 0.868 g/cm2 to 0.856 g/cm2 (P = 0.02), but not at the lumbar site. The HR-pQCT analysis demonstrated a significant reduction of the trabecular BMD from 152.62 mg HA/ccm to 150.80 mg HA/ccm (P &lt; 0.0001) at the tibia site and from 159.09 mg HA/ccm to 156.25 mg HA/ccm (P &lt; 0.0001) at the radius site. No change in bone structure have been observed at 3 months post-transplantation with the HR-pQCT analysis.

CONCLUSION
HR-pQCT is sensitive enough to show a significant decrease of BMD at the trabecular site, as soon as 3 months after transplantation compared to DEXA at the lumbar spine. However, no change in bone structure nor cortical bone volume has been observed. The sensibility of this technique might be higher than DEXA. The rapid assessment of bone structure (3 months post-transplantation) might be too soon to evaluate such abnormalities. Detecting properly rapid changes in bone density, as soon as 3 months after renal transplantation seems feasible. The impact on bone health management needs to be further studied.