BACKGROUND: With modern treatments, the effect of juvenile idiopathic arthritis (JIA) on growth may be less than previously reported. Our objective was to describe height, weight and body mass index (BMI) development in a contemporary JIA inception cohort.

METHODS: Canadian children newly-diagnosed with JIA 2005-2010 had weight and height measurements every 6 months for 2 years, then yearly up to 5 years. These measurements were used to calculate mean age- and sex-standardized Z-scores, and estimate prevalence and cumulative incidence of growth impairments, and the impact of disease activity and corticosteroids on growth.

RESULTS: One thousand one hundred forty seven children were followed for median 35.5 months. Mean Z-scores, and the point prevalence of short stature (height < 2.5th percentile, 2.5% to 3.4%) and obesity (BMI > 95th percentile, 15.8% to 16.4%) remained unchanged in the whole cohort. Thirty-three children (2.9%) developed new-onset short stature, while 27 (2.4%) developed tall stature (>97.5th percentile). Children with systemic arthritis (n = 77) had an estimated 3-year cumulative incidence of 9.3% (95%CI: 4.3-19.7) for new-onset short stature and 34.4% (23-49.4) for obesity. Most children (81.7%) received no systemic corticosteroids, but 1 mg/Kg/day prednisone-equivalent maintained for 6 months corresponded to a drop of 0.64 height Z-scores (0.56-0.82) and an increase of 0.74 BMI Z-scores (0.56-0.92). An increase of 1 in the 10-cm physician global assessment of disease activity maintained for 6 months corresponded to a drop of 0.01 height Z-scores (0-0.02).

CONCLUSIONS: Most children in this modern JIA cohort grew and gained weight as children in the general population. About 1 in 10 children who had systemic arthritis, uncontrolled disease and/or prolonged corticosteroid use, had increased risk of growth impairment.