Explanation

Juvenile onset arthritis (JOA) is a type of arthritis that only kids get.

'Juvenile' means child or young person, and 'onset' means when it starts. You might also hear people call it juvenile idiopathic arthritis (JIA), juvenile chronic arthritis (JCA) or juvenile rheumatoid arthritis.

JOA is a problem with one or more of your synovial joints. It becomes inflamed, so it swells and becomes irritable, and the amount of synovial fluid increases inside. The synovial membrane is swollen and sensitive, and the cartilage becomes thinner. Your joint then can't work as well, because your bones are not well protected or lubricated. This makes your joints feel stiff, and when you move them they hurt.

There are three main types of JOA, depending on how much of your body is affected:

Oligoarticular JOA

Polyarticular JOA

Systemic JOA

Oligoarticular JOA

This is the type of JOA that you are most likely to get - about half of kids with JOA have this type. It affects four or fewer joints, and is sometimes called pauciarticularJOA - both oligo and pauci mean 'a few'. OligoarticularJOA usually affects your larger joints, like your knees, wrists and ankles. Sometimes it might also cause uveitis.

Polyarticular JOA

This affects about 30% of kids with JOA. Poly means 'many' - polyarticularJOA affects five or more joints. It affects the small joints in your fingers, as well as larger ones like your knees, hips and ankles.

When it is very bad, it can be difficult to use the affected joints. So, you might have trouble moving around if the problem is with your knees, or difficulty writing if your fingers are affected. You may also get a fever on these days, and feel tired and unwell. You could also develop a rash on part of your skin, and you might get uveitis.

Systemic JOA

This is the most unusual type of JOA - only about 20% of kids with JOA have it. It is also called Still's disease and it affects your whole body. Periods of 'active' disease can last up to 2 weeks, and during that time you could feel very ill.

It can affect lots of joints, and these will feel stiff and painful, especially in the morning. You will probably get both a high fever and a rash, which are usually worse in the afternoon or evening, when you'll have a high temperature, and pink/white splotches over larger parts of your skin. You'll probably also get enlarged lymph glands - like the ones in your neck. Systemic JOA can make you feel generally sick, tired and fed up.