THU0548 ASSOCIATIONS BETWEEN: MARKERS OF BONE TURNOVER AND RADIOLOGICAL FINDINGS IN CHILDREN DIAGNOSED WITH JUVENILE IDIOPATHIC ARTHRITIS

Abstract

Background Although many children attending pediatric rheumatology departments are diagnosed with low bone mineral density on the basis of clinical imaging, it is difficult to determine which patients have the higher risk of developing osteoporosis as the secondary disease. Recently performed studies involving rheumatological patients have proposed numerous serological indicators for better evaluation of the disease activity. These include markers of bone turnover, among others: bone alkaline phosphatase and osteoprotegerin (which are more specific for bone formation) and also beta isomerized carboxy terminal telopeptide of type I collagen, also known as Beta-Crosslaps (which is considered as an indicator of bone resorption). Objectives The main objective of the study was to evaluate the clinical usefulness of measuring serum concentrations of the selected markers of bone turnover in juvenile idiopathic arthritis (JIA) patients and assess their potential significance in prevention of osteoporosis in these children. Methods Study involved 59 children previously diagnosed with JIA (mean age at diagnosis: 9.0±4.3 years, mean age at study baseline: 12.7±3.9 years). All patients underwent Dual X-Ray Absorptiometry (DXA) examinations in order to assess bone mineral density. Wrist radiographs were also taken for evaluation according to the Steinbrocker classification. The presence of abnormalities in these tests was chosen as the criterion to divide patients into subgroups to perform group comparisons for the serum levels of markers of bone turnover: bone alkaline phosphatase, osteoprotegerin and Beta-Crosslaps. Results According to the Steinbrocker classification, 10 (16.9%) patients were staged as class I or higher. These children had significantly lower serum levels of bone alkaline phosphatase (p=0.0333) than patients with no radiological changes on wrist radiographs. The non-zero Steinbrocker subgroup had also lower Total Body Less Head Z-Score results (p=0.010) than the remaining patients. The DXA results, expressed as Total Body Less Head and Lumbar Spine Z-Score, disclosed low bone mineral density in 10 (16.9%) and 12 (20.3%) patients, respectively. There were no significant correlations between serum levels of markers of bone turnover and bone mineral density measurements. However, bone alkaline phosphatase and osteoprotegerin were negatively correlated with DXA muscle mass (r=-0.359 p=0.040 for bone alkaline phosphatase, r=-0.372 p=0.0392 for osteoprotegerin). Similar correlation was found for bone alkaline phosphatase and DXA fat mass (r=-0.418 p Although Beta-Crosslaps appeared to be the only marker of bone turnover significantly (p=0.0410) associated with Juvenile Arthritis Disease Activity Score 27-Joint Count (JADAS27), it was independent from radiological findings involved in the analysis. However, serum levels of Beta-Crosslaps were higher in patients evaluated in summer than in those assessed in winter (p=0.0464). Radiological findings were not season-variable. Conclusion Low serum concentration of bone alkaline phosphatase seems to be a risk factor for low bone mineral density and, by extension, for osteoporosis. Therefore it should be considered as an important laboratory test in JIA patients suspected of secondary osteoporosis. Clinical significance of osteoprotegerin and Beta-Crosslaps needs to be further investigated. Disclosure of Interests None declared