Objective: To determine the frequency of low bone mineral content (BMC) and low bone mineral density (BMD) as long-term complications in adolescents with early-onset juvenile idiopathic arthritis (JIA), and to identify disease variables, patient characteristics, and biochemical bone markers related to low bone mass.
Methods: One hundred five (87%) of 121 adolescent patients with early-onset JIA (ages 13-19 years, 80 girls and 25 boys, mean age at onset of JIA 2.8 years), from a cohort first admitted to the hospital between 1980 and 1985, were assessed after a mean disease duration of 14.2 years. BMC and BMD of the total body, the lumbar spine at L2-L4, and the femoral neck were measured by dual-energy x-ray absorptiometry. Age- and sex-specific reference values from a pooled, healthy reference population were used to calculate Z scores. Low bone mass was defined as a Z score less than -1 SD.
Results: Among the 103 adolescent JIA patients who underwent total-body imaging, 41% had low total-body BMC and 34% had low total-body BMD. Compared with adolescent JIA patients who had normal total-body BMC, those with low BMC had lower mean weight (P < 0.001), height (P < 0.001), lean mass (P < 0.001), and remission rates (P = 0.016), had longer duration of active disease (P = 0.013), had higher numbers of active and mobility-restricted joints (P < 0.001 and P = 0.001, respectively), had more disability (P = 0.011), had higher frequencies of joint erosions (P < 0.001), and had higher erythrocyte sedimentation rates (P = 0.033). In multiple linear regression analyses of total-body BMC, 88% of the variance was explained by the duration of active disease, the number of joints with restricted mobility, the bone area, urinary deoxypyridinoline values, age, weight, and height.
Conclusion: Forty-one percent of the adolescents with early-onset JIA had low bone mass >11 years after disease onset. The development of low total-body BMC was related to the duration of active disease, disease severity, measures of bone resorption, weight, and height.