Bone mass and quality in patients with juvenile idiopathic arthritis: longitudinal evaluation of bone mass determinants using dual energy X-ray absorptiometry, peripheral quantitative computed tomography, and quantitative ultrasonography

Our objective was to evaluate longitudinally the main bone mass and quality predictors in young juvenile idiopathic arthritis (JIA) patients using lumbar spine dual energy X-ray absorptiometry (DXA) scan, radius peripheral quantitative computed tomography (pQCT), and phalangeal quantitative ultrasonography (QUS) at the same time.In total, 245 patients (172 females, 73 males; median age 15.6 years: 148 oligoarticular, 55 polyarticular, 20 systemic, and 22 enthesitis-related-arthritis (ERA) onset) entered the study. Of these, 166 patients were evaluated longitudinally. Data were compared with two age- and sex- matched control groups.In comparison to controls, JIA patients, but not with ERA, had a reduced spine bone mineral apparent density (BMAD) standard deviation score (P < 0.001) and musculoskeletal deficits, with significantly lower levels of trabecular bone mineral density (TrabBMD) (P < 0.0001), muscle cross-sectional area (CSA) (P < 0.005), and density-weighted polar section modulus (SSIp) (P < 0.05). In contrast, JIA showed fat CSA significantly higher than controls (P < 0.0001). Finally, JIA patients presented a significant reduced amplitude-dependent speed of sound (AD-SoS) (P < 0.001), and QUS z-score (P < 0.005).Longitudinally, we did not find any difference in all JIA patients in comparison to baseline, except for SSIp value that normalized. Analyzing the treatments, a significant negative correlation among spine BMAD values, TrabBMD, AD-SoS and systemic and/or intra-articular corticosteroids, and a positive correlation among TNF-alpha-blocking agents and spine BMAD, TrabBMD, and AD-SoS were observed.JIA patients have a low bone mass that, after a first increase due to the therapy, does not reach the normal condition over time. The pronounced bone deficits in JIA are greater than would be expected due to reduction in muscle cross-sectional area. Thus, bone alterations in JIA likely represent a mixed defect of bone accrual and lower muscle forces.