Systemic Onset Juvenile Idiopathic Arthritis (SoJIA) mimicking Incomplete Kawasaki Disease in a 5-year-old

A 5-Year-Old male presented with 9 days of fever, rash, and poorly described muscle/joint pain despite multiple outpatient visits and treatment with antibiotics for presumed streptococcal pharyngitis, and acute otitis media.In the emergency department he appeared ill with cracked red lips, delayed capillary refill, joint and muscle pain, tachycardia, and a blanchable maculopapular rash coalescing into plaques.Laboratory tests demonstrated leukocytosis, elevated C-reactive protein, thrombocytosis, and hypoalbuminemia.Given the labs, prolonged fever, and mucocutaneous symptoms, he was treated for incomplete Kawasaki Disease with intravenous immunoglobulin (IVIG) and aspirin.Upon admission, echocardiogram and electrocardiogram were both within normal limits.The patient had continued fevers despite IVIG and was given a second dose, which he was also refractory to.Systemic steroids were started and relieved the fever, rash, and joint pains.He clinically improved and was discharged on a corticosteroid taper and aspirin.He was readmitted two weeks later with fever, weight loss, malaise, migratory arthralgias/myalgias, and splenomegaly.Given the persistent fevers and weight loss, hemophagocytic lymphohistiocytosis and malignancy were excluded.He was started on NSAIDs and markedly improved.Given this improvement the diagnosis of juvenile idiopathic arthritis was made.This case highlights the diagnostic overlap between Kawasaki disease and systemiconset juvenile idiopathic arthritis, particularly early in the disease course when fever pattern, rash characteristics, and arthritis may be non-specific.Persistent fever and musculoskeletal symptoms despite IVIG treatment should prompt consideration of other diagnoses causing systemic inflammation, including systemic-onset juvenile idiopathic arthritis.