Systemic Juvenile Idiopathic Arthritis and arthralgia - can it be diagnosed early within the window period? – An observation of serum biomarkers and analysis with other differential conditions in children

Background: Systemic juvenile idiopathic arthritis (sJIA)is a cause of persisting arthralgia which is often missed. Diagnosing sJIA can be challenging, especially when overt arthritis is absent at presentation, highlighting the need for a diagnostic biomarker. Few recent studies have assessed potential biomarkers for sJIA, however, there is no consensus in detecting early. We conducted a study evaluating serum IL-1, IL-6, IL-18, S100A8, and S100A9 as potential diagnostic markers to distinguish sJIA from other conditions presenting as joint pain in children. Methods: A prospective study was conducted in our institute from May-2019 to October-2020 in children under 16 years, who had persisting arthralgia. Serum concentrations of IL-1, IL-6, IL-18, S100A9, and S100A8 were determined using ELISA kits. Receiver operating curve (ROC) analysis was used to determine the cut-off values for IL-1, IL-6, IL-18, S100A8, and S100A9 for differentiating sJIA from other causes of joint pain and fever. Results- Out of 47 children who presented with joint pain and fever 19 of them were eventually diagnosed with sJIA. In the other 28 children, arthralgia and fever was attributed to conditions other than sJIA (non-sJIA). The non-sJIA group comprised children with acute lymphoblastic leukemia, hemophagocytic histiocytosis, systemic lupus erythematosus, Kawasaki disease, Kikuchi disease, and inflammatory bowel disease. Serum levels of IL-18, S100A8, and S100A9 were significantly higher in patients with sJIA compared to the non-sJIA group (p<0.05). The area under the curve (AUC) was significant for IL-18(77.9%), S100A8 (74.9%), and S100A9(71.2%). A serum IL-18 cut-off level of > 2030.45 pg/ml was useful for differentiating between sJIA and other diseases with a sensitivity of 66.67% and specificity of 75.86% for the diagnosis of sJIA. Conclusion- Serum IL-18, S100A8, and S100A9 can be useful in differentiating sJIA early from other causes of persisting arthralgia in children provided with appropriate identification of symptomatology and suspicion.