RESUMO
Early diagnosis of systemic juvenile idiopathic arthritis (s-JIA) is a prerequisite for therapeutic efficacy. However, it is often challenging because most patients with s-JIA do not show arthritis at disease onset and are simply diagnosed with fever of unknown origin. Serum ferritin levels have commonly been used to diagnose s-JIA because they increase in patients with this condition by more than 5 times their normal value. However, there are no definite biomarkers for s-JIA, which makes the clinical diagnosis of s-JIA difficult. We report a case of s-JIA in which interleukin (IL)-18 elevation was observed before ferritin elevation at the early phase of s-JIA. We propose serum IL-18 levels as a more useful biomarker for the early diagnosis of s-JIA compared to serum ferritin levels.