Incomplete Kawasaki syndrome followed by systemic onset-juvenile idiopathic arthritis mimicking Kawasaki syndrome

A 3-month-old child was first treated for incomplete Kawasaki syndrome with three cycles of intravenous immunoglobulins and aspirin, then with methylprednisolone which led to fever remission. The same child was re-hospitalized after a 10-month-period of well-being for the suspicion of a new episode of Kawasaki syndrome, which appeared to be immunoglobulin-resistant: extensive testing failed to provide an alternative diagnosis of any infectious or infiltrative disease. Diagnosis of systemic onset-juvenile idiopathic arthritis was postulated upon the long persistence of fever and inflammatory signs, which subsided only after starting corticosteroid treatment.