There are many terms used to describe chronic arthritis in children. These include juvenile rheumatoid arthritis, juvenile chronic arthritis, and juvenile idiopathic arthritis (JIA). Of these, JIA is used most often by specialists in pediatric rheumatology.
About one child in every 1,000 develops some type of juvenile arthritis. These disorders can affect children at any age, although rarely in the first six months of life. It is estimated that around 300,000 children in the U.S. have been diagnosed with JIA.
There are several types of JIA, all involving chronic joint inflammation. This inflammation begins before patients reach the age of 16, and symptoms must last from six weeks to three months in order to be called chronic. JIA may involve one or many joints and can cause other symptoms, such as fevers, rash, and eye inflammation.
Types of JIA include:
- Systemic onset JIA,which affects about 10% of children with arthritis. It begins with repeating fevers, often accompanied by a pink rash that comes and goes. It may cause inflammation of the internal organs as well as the joints.
- Oligoarticular JIA, which involves fewer than five joints in its first stages and affects about half of all children with arthritis. Girls have a higher risk than boys. Children who develop this form of JIA when they are younger than seven years old have the best chance of having their joint disease subside with time, but they are at increased risk of developing an inflammatory eye problem.
- Polyarticular JIA, which affects five or more joints and can begin at any age. Children diagnosed with polyarticular JIA in their teens may actually have the adult form of RA at an earlier than usual age.
- Psoriatic JIA, which is diagnosed when children have both arthritis and psoriasis—or a strong family history of psoriasis.
- Enthesitis related JIA, which often involves attachments of ligaments as well as the spine. These children more often have joint pain without obvious swelling and may complain of back pain and stiffness.
It is not known what causes the immune system to malfunction in JIA. Malfunctioning of the immune system in JIA targets the lining of the joint, known as the synovial membrane. This causes inflammation. When the inflammation persists, joint damage may occur. According to patient–fact sheet writer Leslie S. Abramson, MD, “Research suggests that some individuals have a genetic tendency to JIA but develop the condition only after exposure to an infection or other unknown trigger.”