Bone mineralization and bone mineral metabolism in children with juvenile rheumatoid arthritis

Objective. To identify mechanisms of the osteopenia associated with juvenile rheumatoid arthritis (JRA) by determining parameters of bone mineralization, and bone mineral content and density (BMC and BMD), in children with JRA. Methods. BMC and BMD were measured by dual x-ray absorptiometry in 41 children with JRA and 62 healthy children. Serum samples were analyzed for concentrations of minerals, vitamin D, parathyroid hormone, osteocalcin, bone-specific alkaline phosphatase (BAP), procollagen I carboxy-terminal propeptide, and tartrate-resistant acid phosphatase (TRAP), and urinary excretion of deoxypyridinoline crosslinks and calcium. Results. BMD was decreased at all sites in JRA patients, BMD, corrected for age, height, weight, and bone area, was decreased at cortical bone sites (1/3 radius, upper and lower extremities, and whole body). Low concentrations of osteocalcin and BAP suggested reduced bone formation, and low TRAP levels suggested decreased resorption. Clinical scales of disease severity were negatively correlated with measures of bone mass. Laboratory markers of disease severity were highly correlated with decreases in markers of bone formation, but not with those of resorption. Although laboratory findings were similar for children with oligoarticular and polyarticular disease, differences in bone mass were greater in children with polyarticular disease. Conclusion. These data suggest an association between decreased bone mineralization in JRA and low bone formation that is related to disease severity. Efforts to stimulate bone formation, therefore, need to be considered clinically in prepubertal children with active JRA.