Background Cartilage oligomeric matrix protein(COMP) is a marker of cartilage metabolism. Serum COMP levels has been found to be lower in children with juvenile idiopathic arthritis (JIA) compared to healthy controls and to increase due to remission [1,2]. It is also found to correlate with joint space narrowing and joint erosions assessed by radiography in children with JIA . We have previously reported that ultrasonography(US) is a reliable method to asses joint cartilage thickness(Cth) in children. These findings and the knowledge of COMP being a part of cartilage matrix make it relevant and possible to investigate the relation between COMP and Cth.
Objectives The aim of this study was to investigate correlation between serum COMP levels and Cth assessed by US in children with JIA.
Methods We examined 85 Danish JIA patients. Subsets of JIA were: 13 systemic onsets, 22 RF-negative, 7 RF- positive polyarticular, 12 extended and 31 persistent oligoarticular JIA. Mean age (range) 10,5 years (5-15), girls/boys 60/25. Blood samples were collected the same day of performed US. CRP, SR, RF, ANA were obtained by routine laboratory analysis and serum-COMP levels were measured by ELISA (Anamar,Sweden). Cth was measured by greyscale US in both knees, wrists, ankles, 2nd MCP-joints and 2nd PIP-joints, and mean Cth of the ten joints was calculated for each patient. Joint-activity described as heat, swelling, pain and limitation of motion was assessed by an experienced pediatric rheumatologist.
Results Asignificant positive correlation was found by linear regression analyses between COMP and mean Cth in patients with activity (p=0.03) when controlling for age and gender (R2=0.28). This was also present in patients with polyarticular subtype (p=0.02), but was not found in other subtypes or patients without joint activity. CRP and SR were significantly higher in patients with joint activity than in patients without (p=0.03). Serum COMP levels were found independent of sex, age, disease duration, systemic steroid treatment, height, weight, BMI, JADAS10, CRP, SR and ANA or RF status. No difference in mean COMP levels was found between the groups with and without activity (p=0.82).
Conclusions Mean COMP levels did not differ with status of disease activity. In patients without activity COMP does not correlate with mean Cth of the examined joints. In patients with activity COMP correlates positively with mean Cth of the examined joints. The positivity of the correlation might indicate that COMP levels in active disease reflects the amount of articular cartilage at the present time.
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T Urakami et al. Clinical significance of decreased serum concentration of cartilage oligomeric matrix protein in systemic juvenile idiopathic arthritis. J Rheumatol 2006;33:5
B.E. Gilliam et al. Measurement of biomarkers in juvenile idiopathic arthritis patients and their significant association with disease severity: a comparative study. Clin Exp Rheumatol 2008;26:492-497
A Spannow et al: Ultrasound and MRI measurements of joint cartilage in healthy children: a validation study. Ultraschall Med. 2011 Jan,32 Suppl 1:S110-6
Disclosure of Interest None Declared
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