[Relationship between bone mineral content and growth disorders in children with juvenile idiopathic arthritis]

In chronic inflammatory processes in children efforts are made to evaluate bone mineral content (BMC) with the use of densitometric parameters, which at the same time determine equivalent of lean body mass (LBM). This functional analysis of the musculoskeletal system by using DXA method seems to be particularly useful for the examination of bone mass in children suffering from juvenile idiopathic arthritis (JIA). THE AIM OF THE STUDY was to assess body mass content having regard of the BMC/LBM ratio in JIA children, depending on the degree of growth inhibition, disease advancement phase and the therapy applied.

The study comprised 97 children aged 5-18 (mean age 12.7+/-3.8 years), 45 girls and 52 boys with diagnosed JIA according to ILAR criteria of 1997. The average duration of disease was 4.1+/-3.1 years. Antropometric and densitometric measurement was made in every child. Body height was defined by Standard Deviation Height Velocity Score - SDHVS (SDS). Patients were divided into 2 groups: I - 28-group with SDS ratio < -2.0; 11 - 69 children with normal height. For the evaluation of disease development and advancement of anatomic changes in joints criteria of Steinbrocker were applied: I grade - without joint damage, II - insignificant or moderate joints damage, III-IV - established deformation. The densitometric research was conducted with the use of double-energy X-ray absorptiometry (DXA) method. Bone mineral density (BMD) was assessed in the whole skeleton (TB BMD), in the vertebras L2-L4 (SB MD), Z-score index for SBMD and BMC, LBM, TB BMC/LBM defined by the Z-score index and compared to norms for age and growth.

Bone mineral density defined as Z-score index for SBMD <-2.0 was reported in 21 children (21.6%). Muscle-skeletal Z-score index for TB BMC/LBM in relation to norms of gender and growth lower than -1.0 was proved in 23 children (23.6%). Considerably lower Z-score index for TB BMC/LBM (p < 0.01) characterized children with growth inhibition and children with significant joints damage (p < 0.02). There was no significant correlation between densitometric parameters and applied treatment with glucocorticoids and without glucocorticoids.

Decrease of bone mineral mass defined as muscle-skeletal Z-score index for TB BMC/LBM was found in almost quarter of patients within the group of JIA children. In the group of children with growth deficiency and with larger joints damage bone mass was significantly lower.