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Juvenile Idiopathic Arthritis - Classification

Juvenile idiopathic arthritis (JIA) is the commonest cause of chronic arthritis in children in many parts of the world (UK, North America, Sub-Saharan Africa, India, Asia, South America). In some parts of the world (e.g., North Europe and North east USA), Lyme disease is common but does not occur in New Zealand.

The incidence is 1 in 10,000 per year and prevalence is 1 in 1,000 - this is similar to epilepsy in children. There are approximately 12,000 children with JIA in the UK, 350,000 in Sub-Saharan Africa and likely over 1 million in India. There is likely more than 2 million children around the world with JIA and many are undiagnosed.

The term JIA covers a group of diseases, 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 rarely is familial. 

The classification of JIA is essentially based on onset, clinical features 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 with more information for each JIA subtype being available. This knowledge is useful as the JIA subtype broadly determines the management approach. 

The classification of Juvenile Idiopathic Arthritis, with clinical criteria

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 or 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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