Juvenile idiopathic arthritis (JIA), sometimes called juvenile rheumatoid arthritis or juvenile chronic arthritis, is a childhood disease that causes inflamed, swollen joints that are often stiff and painful. Symptoms common to all forms of JIA include joint pain, a disturbance in the way a child walks (abnormal gait), and joint stiffness that lasts longer than 1 hour in the morning.
The cause of JIA is not well understood. Most experts believe it is caused by a combination of factors, including an overly active immune system.
There are several types of JIA. Each type is based on how many joints are affected during the first 6 months of active disease, whether the child has other symptoms, and which parts of the body are affected.
- Oligoarticular JIA (oligoarthritis) is the most common type of JIA. In this type, 1 to 4 joints are affected in the first 6 months of the disease. If 4 or fewer joints continue to be affected, it is called persistent oligoarthritis. If more joints become affected after 6 months, it is called extended oligoarthritis.
- Polyarticular JIA (polyarthritis) is the second most common type. Children with this type have 5 or more joints affected in the first 6 months of the disease.
- If an antibody called rheumatoid factor is present in the blood, the polyarthritis is rheumatoid factor-positive (RF-positive).
- If the rheumatoid factor antibody is not present, the polyarthritis is rheumatoid factor-negative (RF-negative).
- Systemic JIA can cause whole-body symptoms, such as fever and rash.
- Enthesitis-related JIA can affect joints and also entheses (the areas where tendons and ligaments attach to the bones).
- Psoriatic JIA can combine joint pain and swelling with a skin condition called psoriasis.
- 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.
Several types of JIA can also include serious eye inflammation.