Bone health in juvenile idiopathic arthritis compared with controls based on a Norwegian observational study.

Background: Children with juvenile idiopathic arthritis (JIA) are at risk for impaired bone health. This study evaluates bone mineral density (BMD) and potential risk factors for reduced BMD.

Methods: In the NorJIA study, Norwegian children with JIA, and age-matched and sex-matched controls participated in a multicentre cohort study with clinical examinations, questionnaires, imaging and blood tests. BMD was measured using dual-energy X-ray absorptiometry and adjusted for bone age. Standard descriptive statistics and t-tests were used.

Results: 205 children with JIA had BMD measured at two study visits, 2 years apart and 125 controls at the second visit. At visit 2, median age was 14.7 years (IQR 11.5-16.6). Median disease duration was 6.6 (IQR 4.7-10.4) years, 50.7% had used or were currently using biologic disease-modifying antirheumatic drugs and 25.9% had ever used systemic steroids. There were no substantial differences in BMD Z-scores between the JIA group and controls. Mean BMD Z-score L1-L4 in JIA was 0.0 (95% CI -0.1, 0.1) and in controls 0.1 (95% CI -0.1, 0.3). A robust association was seen between physical activity levels and BMD. In children with JIA, the mean BMD Z-score L1-L4 was -0.3 (95% CI -0.6, 0.0) in the low-activity group and 0.2 (95% CI 0.0, 0.4) in the high-activity group, with a similar trend in controls. Children with JIA were as physically active as controls.

Conclusions: BMD Z-scores in JIA were similar to controls and positively associated with physical activity. This underlines the importance of early disease control, steroid-sparing medications and physical activity to optimise bone health.

Trial Registration Number: NCT03904459.