Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


A Critical Appraisal of Lumbar Spine DXA Bone Mineral Density in a Longitudinal Study of Children with JIA.

Leffler1,  Maureen G., Shults6,  Justine, Mostoufi-Moab2,  Sogol, Zemel7,  Babette S., Dubner5,  Sarah E., Leonard4,  Mary B., Burnham3,  Jon M.

AI duPont Hospital for Children, Thomas Jefferson University
Children's Hospital of Philadelphia
Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Center for Clinical Epidemiology and Biostatistics, Philadelphia, PA
Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Center for Clinical Epidemiology and Biostatistics
Seattle Children's Hospital, University of Washington School of Medicine
University of Pennsylvania School of Medicine, Center for Clinical Epidemiology and Biostatistics
University of Pennsylvania School of Medicine, Children's Hospital of Philadelphia

Background:

Juvenile idiopathic arthritis (JIA) is associated with vertebral fractures. Precise screening methods are needed to identify those at-risk. Lumbar spine posterior-anterior (PA) dual x-ray absorptiometry (DXA) areal bone mineral density (aBMD, g/cm2), obtained in 2D, is confounded by short stature and superimposes trabecular (vertebral body) and cortical (posterior elements) structures. Volumetric imputation using bone mineral apparent density (BMAD) or height Z-score adjustment (HAZ-aBMD) addresses confounding by stature. 3D width-adjusted volumetric BMD (WA-BMD, g/cm3) pairs PA and lateral scans to isolate the vertebral body, excluding posterior elements. To evaluate the performance of these DXA measures in JIA, we assessed 1) aBMD, BMAD, HAZ-aBMD, and WA-BMD Z-score deficits and their change from baseline to 12 months, and 2) determinants of WA-BMD Z-scores and their change.

Methods:

JIA subjects [n=88, 5 –19 yr, 79% F, 21 oligoarticular (OJIA), 35 polyarticular (PJIA), 16 systemic (SJIA), 16 spondyloarthropathy (SpA)] completed two visits. JIA subjects were compared with controls (n = 909, 5–21 yr). DXA PA spine (L1–4) scans (Hologic Delphi) were used to calculate aBMD and BMAD [bone mineral content/(bone area)1.5] and paired PA – lateral scans of L3 were used to determine WA-BMD. DXA Z-scores, derived from controls, were age-, sex- and race-specific. HAZ-aBMD Z-score was calculated according to Zemel et al. (J Clin Endocrinol Metab, 2010). T-tests and multivariable linear and logistic regression were used to compare Z-scores and identify predictors of low Z-scores (< -1).

Results: Baseline:

Compared with controls, height Z-scores were low in JIA (0.26 vs. -0.06, p = 0.001). In JIA, deficits were observed using WA-BMD (Z =-0.59, p < 0.001), but not aBMD (Z =-0.23, p = 0.05), HAZ-aBMD (Z =-0.14, p = 0.62), or BMAD (Z =-0.13, p = 0.27). WA-BMD deficits were significant in PJIA, SJIA and SpA. Lower WA-BMD Z-scores were associated with low BMI Z-scores (JIA and controls, p < 0.001), low height Z-scores (JIA only, p for interaction < 0.04), steroid use, active arthritis, and high CHAQ scores (p < 0.05).

Follow Up:

No significant changes were noted for JIA using any DXA measure. WA-BMD Z-scores improved in SpA only (D = 0.46, p = 0.02). aBMD, HAZ-aBMD and BMAD Z-scores improved in SJIA (D = 0.18 – 0.21, p < 0.05). Adjusting for baseline WA-BMD Z-scores (b =-0.58, p < 0.001), no clinical predictors of Z-score changes were detected, but older age was associated with significant improvement (Figure).

Conclusions:

In JIA, WA-BMD detects spine deficits obscured using aBMD, HAZ-aBMD, and BMAD. Greater baseline deficits were associated with low BMI and height Z-scores, active disease, disability, and steroid use. WA-BMD improvements were greatest in adolescents and those with lower baseline Z-scores. Future studies should use 3D modalities to define which tool best identifies vertebral fragility in JIA.

To cite this abstract, please use the following information:
Leffler, Maureen G., Shults, Justine, Mostoufi-Moab, Sogol, Zemel, Babette S., Dubner, Sarah E., Leonard, Mary B., et al; A Critical Appraisal of Lumbar Spine DXA Bone Mineral Density in a Longitudinal Study of Children with JIA. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :206
DOI: 10.1002/art.27975

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