Similarities and Differences between Systemic Juvenile Idiopathic Arthritis and Kawasaki Disease

Systemic juvenile idiopathic arthritis (SJIA) is an autoinflammatory disease characterized by fever, rash, and arthritis. In actual practice, SJIA is sometimes confused with Kawasaki disease (KD), as they share clinical and laboratory findings. Compared to those with KD, patients with SJIA present with more frequent joint symptoms and organ dysfunction and have more severe overall laboratory findings. However, it is important to note that clinical and laboratory findings of SJIA can also occur in severe forms of KD. Hyperferritinemia and elevated interleukin (IL)-18 levels are highly specific for SJIA and can serve as useful biomarkers for differentiating SJIA from KD. The most significant difference between SJIA and KD is the chronic nature of the disease course. Therefore, the possibility of overlooked SJIA should be considered in patients with KD who present with recurrent fever, rash, or arthritis. Approximately 0.5% of patients with KD are ultimately diagnosed with SJIA. Although the relationship between SJIA and KD is still partially understood, it will be an interesting and important research topic for KD-like hyperinflammatory diseases, including SJIA and KD.