A rheumatic disease of childhood that most commonly affects children between the ages of 2–4 years. Diagnosis requires arthritis involving ≥ 1 joint, intermittent fever that lasts for at least 2 weeks with fever spikes occurring on at least 3 consecutive days, and ≥ 1 extra-articular manifestation (e.g., salmon-pink rash, generalized lymphadenopathy, splenomegaly/hepatomegaly, serositis).