Background Juvenile idiopathic arthritis (JIA) is one of the most common and most disabling rheumatic diseases in children. JIA is a systemic chronic inflammatory immunopathological disease, which leads to dysfunction of the joints, their deformation and limitations of life of the child, violates the child's growth and development. One of the complications of systemic JIA in children is osteoporosis. In the pathogenesis of osteoporosis important place is given to the use of glucocorticoids. In world Rheumatology successfully used drugs aimed at the major pro-inflammatory cytokines such as tumor necrosis factor (TNF), interleukin-1 (IL-1), interleukin-6 (IL-6), and others.

Objectives The purpose of research - to determine the influence of biological therapy on bone mineral density in children with JIA.

Methods 15 children with systemic JIA (mean age 11,9±3,4 years) were examined in the rheumatological department of 4th city clinical hospital of Minsk.

Bone mineral density was assessed by 2-energy X-ray absorptiometry (DEXA) at two points of the skeleton. The level of mineralization of skeletal mineral content was estimated in the bone tissue (BMC), bone mineral density (BMD) and the parameter Z-score. Z-score was used to determine the incidence of osteopenia and osteoporosis in children surveyed. In accordance with the WHO criteria for normal bone mineral density was diagnosed with the Z-score> -1 SD, osteopenia - at Z-score <-1 SD, but> - 2,5 SD, osteoporosis - with Z-score <-2,5 SD. Statistical data processing carried out using an integrated application package “Statistics 6 for Windows”.

Results In a study of children osteopenia was diagnosed in 9 patients with systemic JIA (mean Z-score -2,3 SD) Osteoporosis was diagnosed in 6 patients with systemic JIA (mean Z-score -2,7 SD). All children received a mean dose of methotrexate 12.7 mg/m² of body surface area, an average dose of methylprednisolone 0.34 mg/kg body weight per day and treatment of IL-6 inhibitor - tocilizumab 8 mg/kg body weight every 2–4 weeks. Bone mineral density was measured prior to initiating therapy tocilizumab and after 2 years of therapy.

During tocilizumab therapy achieved remission of the disease, all children was canceled methylprednisolone. After re densitometry of 2 years after the beginning of therapy improvement noted tocilizumab Z-score in children with osteopenia with Z-score -2.3 SD to Z-score -1.4 SD, in children with osteoporosis a Z-score -2 7 SD to Z-score - 2,1 SD.

Conclusions The results indicate a positive influence tocilizumab therapy to bone mineral density in children with JIA.

Acknowledgements This study would not have been possible without the collaboration of numerous Belarusian pediatric rheumatologists, patients and their parents.

Disclosure of Interest None declared