Serum calprotectin and joint ultrasound in the definition of disease relapse in non-systemic juvenile idiopathic arthritis: a prospective longitudinal study.

Objectives: The aim of our study was to investigate the role of serum calprotectin (SC) and muscle-skeletal ultrasound (MSUS) as predictive markers of relapse in patients with juvenile idiopathic arthritis (JIA).

Methods: Sixty non-systemic (ns) JIA patients in clinical remission were recruited to evaluate the risk of disease relapse. SC levels and JIA disease activity were assessed at every visit (3, 6, 12 and 18 months). Joint synovitis, characterised by both synovial effusion (SE) and synovial hyperplasia (SH), was measured by US score (sum of SE, SH, power Doppler and bone erosions) given to each examined joint and US ratio (US score/number of joints examined) at every visit. Associations of SC, US score and US ratio with relapse prevalence was studied longitudinally by using generalised estimating equations model.

Results: Thirty-one (51.6%) patients relapsed within 18 months. Patients with higher baseline US scores showed higher risk of relapse at 6 months (OR (95% confidence interval (CI)): 1.96 (1.09-3.52)). Additionally, patients with higher SC values at baseline showed higher risk of relapse at 18 months (1.66 (1.13-2.44)). Patients with higher baseline SC values showed an increased overall odds of relapse up to 18 months of follow-up (1.21 (1.08-1.36)). Furthermore, patients with higher US scores showed an increased overall odds of relapse up to 18 months of follow-up (1.96 (1.56-2.46)). Similarly, patients with higher US ratio showed an increased overall odds of relapse up to 18 months of follow-up (16.62 (7.17-38.54)).

Conclusions: SC was able to identify JIA patients with unstable remission and increased risk of relapse. MSUS represents an interesting additional tool to the clinical evaluation, especially in predicting early relapse.