Juvenile idiopathic arthritis (JIA) is a heterogeneous group of conditions which encompasses all forms of arthritis of unknown etiology lasting for at least 6 weeks and with onset before the age of 16 years.
As a result of the lack of pathognomonic features, the diagnosis of JIA is one of exclusion among all possible causes of chronic arthritis in childhood.
The ILAR criteria for systemic arthritis require the presence of arthritis accompanied or preceded by a documented quotidian fever of at least 2 weeks’ duration, plus at least one of the following: characteristic rash, generalized symmetrical lymphadenopathy, enlargement of liver or spleen, or serositis (pericarditis, pleural or pericardial effusion, rarely peritonitis).