Pediatric bone evaluation with HR-pQCT: A comparison between standard and height-adjusted positioning protocols in a cohort of teenagers with chronic kidney disease.

BACKGROUND: High-resolution peripheral quantitative computed tomography (HR-pQCT) evaluates different components of bone fragility. The positioning and length of the region of interest (ROI) in growing populations remain to be defined. METHODS: Using HR-pQCT at the ultradistal tibia, we compared a single-center cohort of 28 teenagers with chronic kidney disease (CKD) at a median age of 13.6 (range, 10.2-19.9) years to local age-, gender-, and puberty-matched healthy peers. Because of the potential impact of short stature, bone parameters were assessed on two different leg-length-adjusted ROIs in comparison to the standard analysis, namely the one applied in adults. The results are presented as median (range). RESULTS: After matching, SDS height was -0.9 (-3.3;1.6) and 0.3 (-1.4;2.0) in patients and controls, respectively (P<0.001). In younger children (e.g., prepubertal, n=11), bone texture parameters and bone strength were not different using standard analysis. However, using a height-adjusted ROI enabled better characterization of cortical bone structure. In older patients (e.g., pubertal, n=17), there were no differences for height between patients and controls: with the standard evaluation, cortical bone area and cortical thickness were significantly lower in CKD patients: 85 (50-124) vs. 108 (67-154) mm2 and 0.89 (0.46-1.31) vs 1.09 (0.60-1.62) mm, respectively (both P<0.05). CONCLUSIONS: Adapting the ROI to leg length enables better assessment of bone structure, especially when height discrepancies exist between controls and patients. Larger cohorts are required to prospectively validate this analytic HR-pQCT technique.

[Neonatal intoxication to vitamin D in premature babies: A series of 16 cases]. / Intoxication néonatale à la vitamine D chez des anciens prématurés : une série de 16 cas.

INTRODUCTION: Preterm neonates are particularly at risk of vitamin D (25-D) deficiency. To prevent rickets and osteopenia in this population, international guidelines vary between 800 and 1000IU per day of vitamin D in Europe and recommend 400IU per day in the USA. Target levels of circulating 25-D are not well identified, with the lower target level 50-75nmol/L and the upper target level probably 120nmol/L. METHODS: Between 2013 and 2015, 16 premature infants (born<35WG) were referred to pediatric nephrology clinics because of symptoms secondary to 25-D overdose during the neonatal period. Clinical and biological data were retrospectively reviewed to better define this population. The results are presented as the median (range). RESULTS: Gestational age was 27 (24-35)WG with a birth weight of 810 (560-2120)g. Nephrocalcinosis was the initial symptom in 37% of cases, hypercalcemia in 44%, and hypercalciuria in 19%. Daily vitamin D doses were 333 (35-676)IU. Age and body weight at initial symptom were 36.6 (27.6-47.6)WG and 2300 (640-3760)g, respectively. The 25-D level at the time of the first dosage was 210 (119-350)nmol/L and the 1-25 vitamin D level was 370 (245-718)pmol/L (local normal values for age<240). During follow-up, 12 patients displayed nephrocalcinosis, ten hypercalciuria, and three hypercalcemia. The 25-D level normalized in ten patients within 10 (3-32)months after vitamin D withdrawal. Nephrocalcinosis improved in ten of 12 patients, within 12 (3-30)months. Vitamin D could be readministered in ten patients. When searched (n=3), no CYP24A1 mutation was identified in two patients, but was identified in the heterozygous state in one. CONCLUSION: A 25-D overdose should be systematically ruled out in the presence of nephrocalcinosis, hypercalcemia, and/or hypercalciuria during infancy in children born preterm. Studies are required to assess the exact frequency of 25-D deficiency and overdose in this population, as well as to evaluate the potential deleterious effects of this imbalance on bone, kidney, and brain development.