Table 1.

International League of Associations for Rheumatology (ILAR) classification of juvenile idiopathic arthritis: categories, frequency, onset age distribution, and sex prevalence [1]

	Frequencya	Onset age	Sex ratio
Enthesitis-related arthritis	3–11%	Late childhood or adolescence	M>>F
Oligoarthritis	27–56%	Early childhood	F>>>>M
Psoriatic arthritis	2–11%	Biphasic distribution; early peak at 2–4 years and later peak at 9–11 years	F>M
Rheumatoid-factor-positive polyarthritis	2–7%	Late childhood or adolescence	F>>>M
Rheumatoid-factor-negative polyarthritis	11–28%	Biphasic distribution; early peak at 2–4 years and later peak at 6–12 years	F>>M
Systemic arthritis	4–17%	Throughout childhood	F=M
Undifferentiated arthritis	11–21%	–	–

^aReported frequencies refer to percentage of all juvenile idiopathic arthritis

F female, M male