Growth patterns in early juvenile idiopathic arthritis: Results from the Childhood Arthritis Prospective Study (CAPS)

Objectives: To investigate early vertical growth patterns and factors associated with poor growth in a modern inception cohort of UK children with juvenile idiopathic arthritis (JIA) using data from the Childhood Arthritis Prospective Study (CAPS). Methods: A study period of 3 years was chosen. Children included in this analysis had a physician diagnosis of JIA and had height measurements available at both baseline and at three-years of follow-up. Height is presented as z-scores calculated using World Health Organisation growth standards for age and gender. Growth over the three-year period was assessed using change in z-score and height velocity. Univariable and multivariable linear regressions were used to identify factors associated with height z-score at baseline and change of height z-score at 3 years. Results: 568 patients were included; 65% female, median baseline age 7.4 years [interquartile range (IQR) 3.6, 11.2], median symptom duration at presentation 5.5 months [IQR 3.1, 11.6]. Height z-score decreased significantly from baseline to three years (p≤0.0001); baseline median height z-score was -0.02(IQR -0.71, 0.61), decreasing to -0.47(IQR -1.12, 0.24) at three years. Growth restriction, defined as change of height z-score ≤-0.5, was observed in 39% of patients. At 3 years, higher baseline height z-score was the strongest predictor for a negative change in height z-score [-0.3 per unit of baseline height z-score (95% CI -0.36, -0.24), p<0.0001]. Conclusions: Although overall height at 3 years after initial presentation to rheumatology is within the population norm, as a cohort, children with JIA experience a reduction of growth in height over the first 3 years of disease. Late presentation to paediatric rheumatology services is associated with lower height at presentation. However, patients with the lowest height z scores at presentation were also the most likely to see an improvement at 3 years. The impact of JIA on growth patterns is important to children and families and this study provides useful new data to support informed clinical care.