Table 1 Summary of the main features of the six different subtypes of JIA
Subset of JIA | Frequency % | Age at onset | Clinical presentation | Sex |
|---|---|---|---|---|
Oligo | 27–56 | Early childhood, peak 2–4 years | Four or fewer joints involved the first 6 months | F> > M |
Poly RF negative | 11–28 | Early peak 2–4; late peak 6–12 years | Four or more joints involved within the first 6 months, absence of IgM RF. Heterogeneous disease with three subsets. Prognosis varies with the disease subset | |
Poly RF positive | 2–7 | Late childhood-adolescence | Four or more joints involved within the first 6 months, IgM RF positive. Resembles adult RA. Involvement of small joints. Progressive and diffuse joint involvement | F> > M |
Ethesitis related | 3–11 | Late childhood-adolescence | Characterised by enthesitis and arthritis. Often HLA-B27 positive. Commonly hip involvement at presentation. Often a mild and remitting course but may progress with sacroiliac and spinal joint involvement, resembling ankylosing spondylitis | M> > F |
Psoriatic | 2–11 | Early peak 2–4 years; late peak 9–11 years | Arthritis and psoriatic rash or psoriasis in close family. Controversial definition, resembles oligoarthritis but more often with dactylitis and involvement of both small and large joints | F > M |
Systemic | 4–17 | Throughout childhood | Arthritis and quotidian fever plus one or more of the following symptoms: characteristic rash, hepatomegaly, splenomegaly, lymphadenopathy, serositis. Variable course; 5–8 % develop macrophage activation syndrome | F = M |