Table 1 Juvenile idiopathic arthritis subtypes show specific age ranges for disease onset

Systemic onset

Arthritis and daily fever ≥ 3 days, accompanied by at least one of the following: evanescent (non-fixed) erythematosus rash, generalised lymph node enlargement, hepatomegaly or splenomegaly (or both), serositis

4–17

Throughout childhood

1:1

Oligoarticular

Arthritis affecting 1–4 joints during the first 6 months of disease

27–60

Early childhood (peak 2–4 years)

5:1

 Persistent

Arthritis affecting < 4 joints throughout the disease course

40

 Extended

Arthritis affecting > 4 joints after the first 6 months of disease

20

Polyarticular

Arthritis affecting > 5 joints during the first 6 months of disease

 Rheumatoid factor positive

Two or more positive tests for rheumatoid factor at least 3 months apart

2–7

Late childhood or adolescence (peak 12–14 years)

3:1

 Rheumatoid factor negative

Tests for rheumatoid factor negative

11–30

Early peak 2–4 years and late peak 6–12 years

3:1

Juvenile psoriatic arthritis

Arthritis and psoriasis, or arthritis and at least 2 of the following: dactylitis, nail pitting or onycholysis, psoriasis in first degree relative

2–11

Late childhood or adolescence

1:0.95

Enthesitis related arthritis

Arthritis and enthesitis, or arthritis or enthesitis with at least 2 of the following: sacroiliac joint tenderness or inflammatory lumosacral pain (or both), HLA-B27 antigen positive, onset in boy over 6 years old, acute anterior uveitis, HLA-B27 associated disease in first degree relative

1–11

Early peak 2–4 years and late peak 6–12 years

1:7

Undifferentiated arthritis

Arthritis that fulfils criteria in no specific category or meets criteria for more than one category

11–21