Abstract
Background
Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic arthropathy of childhood and is associated with low bone mass, and may hasten the onset of osteoporosis later in life1. Bone loss occurs because of an imbalance between osteoclasts-activating factors like receptor activator of nuclear factor-κB ligand (RANKL) and its inhibitor osteoprotegerin (OPG) 2. Dual energy X-ray absorptiometry (DXA) is the preferred method for measuring bone mineral density (BMD) in children and to identify and follow individuals at risk for fracture 3. The objective is the Evaluation of serum levels of osteoprotegerin and RANKL and their correlation with BMD in JIA patients.
Methods
Forty JIA patients (according to the revised classification criteria of ILAR) and 40 healthy children individually matched for age, sex and race were included in this study. Children excluded from the study were those with primary and secondary causes of osteoporosis (such as chronic illness).
All patients were assessed clinically by: age, sex, body mass index, type of JIA, disease duration and disease activity (by Juvenile Arthritis Disease Activity Score; JADAS 10). The functional disability was assessed by the Childhood Health Assessment Questionnaire (CHAQ). Blood samples were collected from JIA patients and healthy controls to determine serum levels of OPG and RANKL by ELISA. DXA scans were done using GE Healthcare Lunar DPX, Madison, Wisconsin. Bone mineral density of the L1-L4 lumbar spine and total body less head (TBLH) was evaluated in g/cm2 and expressed as Z score for age, sex according to the reference data given for this equipment.
Results
The study included 40 patients (25 females) with a mean age of 11.14 years and median disease duration of 2.5 years. As regard JIA type, 45% of patients were oligoarticular, 32.5% were polyarticular, and 22.5% were systemic JIA. Median JADAS 10 was 13.95. Patients (especially polyarticular JIA) had significantly higher serum RANKL levels and lower serum OPG and OPG/RANKL ratio when compared with controls (with p-value <0.001, 0.032 and <0.001 respectively). A diagnosis of low BMD (BMD Z-score ≤ -2) was given in 25% of patients (15% polyarticular and 10% systemic) by DXA of lumbar spine, and 20% (10% polyarticular and 10% systemic) by DXA of TBLH. On the other hand, no patient was given a diagnosis of osteoporosis (BMD Z-score ≤ -2 and a significant fracture history). Low BMD at lumbar spine and TBLH was negatively correlated with serum RANKL while positively correlated with OPG/RANKL ratio. Moreover, low BMD at lumbar spine was positively correlated with serum OPG level
Conclusion
High RANKL and low OPG levels appear to be associated with low bone mass in JIA patients. Patients with JIA (especially polyarticular and systemic subtype) are at increased risk of low bone mineral mass. Disclosure of Interests None declared
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