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JIA classification

Definition of JIA - The term JIA covers a group of diseases, it is a diagnosis of exclusion, with arthritis for six weeks or more, and the cause is unknown - likely a combination of genetic and environmental factors. JIA is rarely familial. 

The classification of JIA is essentially based on onset and progression (especially the number of joints affected in the first 6 months), and the presence or absence of rheumatoid factor.  

There are several JIA subtypes summarised in the Table below. This knowledge is useful as the JIA subtype broadly determines the management approach. 

The classification of Juvenile Idiopathic Arthritis

Characteristic

Clinical features

Age at onset

<16 years

Minimum duration

6 weeks

Subtypes

Systemic

Arthritis

Fever, rash, adenopathy, serositis

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

•HLA-B27+

•Family history of HLA-B27+ related disease

Psoriatic arthritis

Arthritis and psoriasis or arthritis and at least two of:

•Dactylitis

•Nail changes

•Family history of psoriasis

Undifferentiated

Arthritis not fulfilling the above categories or fulfilling more than one category

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