Monoartrite: artrite idiopatica giovanile o malattia reumatica?

A 9-year-old child presents to the emergency room with fever, pain, and swelling in the right knee. Based on the tests, the onset of pauciarticular rheumatoid arthritis is hypothesized. After further medical history assessment and a cardiology consultation, which reveals aortic valve insufficiency, the diagnosis of rheumatic disease is confirmed.