POS1296 JIA PATIENTS DO NOT HAVE MORE OSTEOPOROSIS THAN HEALTHY AGE AND SEX-MATCHED CONTROLS BUT LOWER BONE MASS DENSITY IS FOUND AT TOTAL HIP AND CORTICAL COMPARTMENT
Authors: M. Lopez Corbeto, M. Barcelo Bru, E. Moreno Ruzafa, M. Pasqual Pastor
Journal: Annals of the Rheumatic Diseases (2021)

Background: Achievement of a normal peak bone mass is an especially important consideration in young adults with juvenile idiopathic arthritis (JIA), because interference with attainment of peak bone mass may not be repaired later in life. It has been suggested that children with JIA cortical appendicular skeletal bone is more affected by disease activity than axial trabecular bone. To evaluate bone mineral density (BMD) DXA measurements are widely used. Although, DXA is limited to two-dimensional evaluation of integral BMD and cannot differentiate between trabecular and cortical bone compartments. Alternatively, 3D-DXA analysis is a new method based on DXA scans of proximal femur that provides accurate estimates of trabecular and cortical volumetric BMD. Objectives: The aim of the study was to analyze the trabecular and cortical bone using 3D-DXA in young adults with JIA compared to age-matched healthy controls. Methods: This cross-sectional study was aimed to analyze the differences in 3D-DXA proximal femur compartments. The patients were recruited from the specialized transitional unit of the Vall d’Hebron University Hospital. JIA patients older than 18 yo without previous bisphosphonates intake were included. Age and sex-matched healthy controls were selected. DXA scans (Lunar Prodigy, General Electric Medical Systems, v.15) were acquired. OP was defined according to the WHO criteria. The 3D-DXA software was used to assess in 3D the trabecular density and cortical thickness from DXA scans as reported previously [1]. The 3D-DXA and DXA measurements were compared using Student’s t test. Categorical variables were compared using Chi-squared test. All hypothesis tests with p value lower than 5% were considered significant. Results: Forty-six patients and 46 age and sex-matched controls were evaluated. The mean time of disease’s duration was 7.37 years, and the most frequent JIA subtype was Oligoarticular ANA positive. More than 21% of the patients had an active disease. OP was present in 5 patients and 1 control. Despite not finding significant differences in the prevalence of osteoporosis, JIA patients had lower aBMD at total hip by DXA and lower cortical sBMD by 3D-DXA than controls (Table 1). Table 1. Comparison of DXA and 3D-DXA measurements between JIA and healthy controls Variable JIA patients (n=46) Healthy controls (n=46) P value DXA Lumbar aBMD (g/cm 2 ), mean ± sd 1.097 ± 0.02 1.155 ± 0.02 0.042 Right femoral neck aBMD (g/cm 2 ), mean ± sd 0.930 ± 0.02 1.014 ± 0.01 0.041 Right total hip aBMD (g/cm 2 ), mean ± sd 0.932 ± 0.02 1.001 ± 0.01 0.008 Lumbar T-score, mean ± sd -0.716 ± 0.16 -0.212 ± 0.16 0.037 Right femoral neck T-score, mean ± sd -0.563 ± 0.17 0.087 ± 0.12 0.036 Right total hip T-score, mean ± sd -0.721 ± 0.18 -0.12 ± 0.13 0.008 3D-DXA Trabecular vBMD (mg/cm 3 ), mean ± sd 180.44 ± 5.54 194.57 ± 5.11 0.064 Cortical sBMD (mg/cm 2 ), mean ± sd 147.23 ± 3.41 161.52 ± 2.89 0.002 Osteoporosis (WHO definition) Yes, n (%) 5 (10.87) 1 (2.17) 0.091 No, n (%) 41 (89.13) 45 (97.83) DXA dual-energy X-ray absorptiometry , sd standard deviation , aBMD areal bone mineral density, 3D-DXA three-dimensional dual-energy X-ray absorptiometry, vBMD volumetric bone mineral density, sBMD superficial cortical bone mineral density Conclusion: JIA patients do not have more OP than controls in our cohort but there are differences in BMD in the different locations and greater involvement of the cortical bone in JIA. References: [1]Brance ML, et al. Trabecular and cortical bone involvement in rheumatoid arthritis by DXA and DXA-based 3D modelling. Osteoporos Int, 2020 Sep 24. Disclosure of Interests: None declared