Poor Correlation Between Disproportionately Higher BMD Z-Scores of the Individual Lumbar Vertebrae By DXA and Vertebral Fractures in Children

Presentation Number: SAT 302
Date of Presentation: April 1st, 2017

Tasma Harindhanavudhi*1, Richard Jones2, Sara Van Nortwick2, Kyriakie Sarafoglou3, Bradley Scott Miller4, Tara Holm2 and Anna Petryk2
1Univ of Minnesota, Minneapolis, MN, 2University of Minnesota, Minneapolis, MN, 3Leo Fung Center for CAH and DSD, Minneapolis, MN, 4University of Minnesota Masonic Children's Hospital, Minneapolis, MN

Abstract

Background: Dual-energy X-ray absorptiometry (DXA) remains the most common mode of bone mineral density (BMD) evaluation in adults and children. In adults, the presence of a disproportionately higher BMD Z-score (>1 SD difference) between the individual lumbar vertebrae could be an indicator of a vertebral fracture and, therefore, warrant further evaluation of the lateral vertebral morphology. However, in children, the skeleton is still growing and undergoing changes in geometry (modeling), introducing developmental aspects as a confounding variable.

Objective: The goal of the study was to correlate the results of a lumbar spine DXA with lateral lumbar spine morphology to elucidate the clinical significance of discrepancies between individual vertebral BMD Z-scores.

Methods: A retrospective chart review identified 360 DXA scans performed between 9/01/2014 and 5/01/2016 in patients <18 years of age. DXA scans were cross-referenced against all lumbar spine x-ray and DX vertebral fracture analysis (DX VFA) database within the 6 months preceding or following the date of a DXA scan. Vertebral fractures were assessed using a semiquantitative method of Genant et al. and defined as a ≥15% loss in the anterior, middle, or posterior height ratio.

Results: Out of 360 DXA scans, 52 (14.4%) had both a vertebral BMD L1-L4 Z-score ≥1 SD difference, and either lumbar spine x-ray or DX VFA. Only two patients (3.8%) with vertebral BMD Z-score ≥1 SD difference had a vertebral fracture at the same site. The most common vertebra with the highest BMD Z-score was L1 (67%), followed by L3 (23%), L2 (8%) and L4 (2%) vertebrae. The vertebrae with the highest BMD Z-score had a normal anatomy. Although helpful as an imaging modality, DX VFA provided images of an inferior quality compared to the radiographs, particularly in younger children.

Conclusions: We conclude that the correlation between the finding of ≥1 SD difference between vertebral BMD Z-scores and vertebral fracture is low. We postulate that variations in BMD Z-scores of otherwise anatomically normal vertebrae reflect differences in the timing of the vertebral growth. Therefore, it does not appear justified to recommend further imaging based solely on the results of a DXA scan without clinically meaningful indications. Moreover, since L1 was the most frequent vertebra with a disproportionately higher BMD Z-score, it may be more appropriate to use L2-L4 average rather than L1-L4 average for reporting BMD Z-scores in children.

 

Disclosure: BSM: Advisory Group Member, Abbvie, Coinvestigator, BioMarin, Coinvestigator, Armagen, Principal Investigator, Alexion, Principal Investigator, Endo Pharmaceuticals, Ad Hoc Consultant, Ferring Pharmaceuticals, Principal Investigator, Genentech, Inc., Principal Investigator, Novo Nordisk, Ad Hoc Consultant, Novo Nordisk, Ad Hoc Consultant, Pfizer, Inc., Ad Hoc Consultant, Sandoz, Principal Investigator, Sandoz, Scientific Content Contributor, Up To Date, Principal Investigator, Versartis, Ad Hoc Consultant, Versartis, Coinvestigator, Shire, Principal Investigator, Tolmar, Coinvestigator, Eli Lilly & Company. Nothing to Disclose: TH, RJ, SV, KS, TH, AP