The classification of JIA is essentially based on the number of joints affected in the first 6 months, disease progression, the presence or absence of rheumatoid factor or systemic features.
There are several JIA subtypes, these are summarised in the Table below. This knowledge is useful as the JIA subtype broadly determines the management approach.
|The classification of Juvenile Idiopathic Arthritis, with clinical criteria|
|Age at onset||<16 years|
|Minimum duration||6 weeks|
|Fever, rash and can also have adenopathy, serositis, hepato and / or splenomegaly.|
|Oligoarthritis||• 1–4 joints affected during the first 6 months.|
|Persistent – affects no more than four joints throughout course.
Extended – affects more than four joints after first 6 months.
|Polyarthritis||Rheumatoid factor positive – affects five or more joints in first 6 months. Rheumatoid factor is positive on at least two occasions with tests taken at least 3 months apart.
Rheumatoid factor negative – affects five or more joints in first 6 months. Rheumatoid factor is negative.
|Enthesitis-Related arthritis (sometimes called ERA)||Arthritis and enthesitis, or arthritis or enthesitis with at least two of the following:
•Sacroiliac joint tenderness.
•Inflammatory back pain.
•Family history of HLA-B27+ related disease.
|Psoriatic arthritis||Arthritis and psoriasis or arthritis and at least two of:
•Family history of psoriasis.
|Undifferentiated||Arthritis not fulfilling the above categories or fulfilling more than one category.|