About 1 out of 1,000 children have juvenile idiopathic arthritis (JIA).
There are several types of juvenile idiopathic arthritis, with most types being
more common in girls.
The types of JIA affect children at
the following rates:
- Up to 60% of children with JIA have oligoarticular arthritis. Of these children, 20% to 30% have symptoms in more than four joints after the first 6 months, so they are said to have extended oligoarticular JIA. The rest of these children continue to have less than four joints affected over time. This is called persistent oligoarticular JIA.
- About 30% of children with JIA have RF-negative polyarticular JIA. This means they have polyarticular symptoms without an antibody called rheumatoid factor in their blood.
- Fewer than 10% of children with JIA have RF-positive polyarticular JIA. This means they have polyarticular symptoms and also have rheumatoid factor in their blood.
- About 10% of children with JIA have systemic symptoms.
- About 10% of children have a form of arthritis called enthesitis-related JIA.
- Fewer than 10% have psoriatic JIA.
- A few children are said to have unclassified JIA. This means that their symptoms and past health do not exactly match any of the other types of JIA.
Juvenile idiopathic arthritis can
occur at higher rates among certain ethnic groups and in some geographic areas.
Environmental and genetic factors are thought to be responsible, though
researchers have yet to confirm this theory.
