About one in 1,000 children has arthritis. Usually it's a form of inflammatory arthritis known as juvenile idiopathic arthritis (formerly known as juvenile chronic arthritis). This is a separate condition from rheumatoid arthritis. In many cases the inflammation stops in late childhood, but about a third of children affected have problems that last into their adult life.

There are three common types of juvenile idiopathic arthritis:

Pauciarticular arthritis
This often starts at the age of two or three. The problem is limited to four joints or fewer, which become swollen and painful. Sometimes the eyes are affected, too.

Polyarthritis
This affects five or more joints. It can start at any age, from a few months onwards, and usually spreads from one joint to another quite quickly. Children often feel generally unwell, sometimes with a fever.

Systemic disease
This affects the whole body and causes fever and rashes as well as inflamed and painful joints. It usually starts in children under five and used to be called Still's disease.

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