Juvenile rheumatoid arthritis (JRA), also called juvenile idiopathic arthritis (JIA), is the most common type of arthritis that occurs in children, affecting 50,000 youth in the U.S. It is defined as at least 6 weeks of persistent arthritis in a child younger than 16 years of age and is characterized by joint inflammation, pain, swelling, redness, and stiffness. It can also damage joints, affect growth, and cause eye problems such as uveitis as well as inflammation of internal organs.
JRA is believed to be an autoimmune disorder. The tendency to develop JRA may be inherited, but it is believed that a triggering event is required for it to emerge, although little is known about what triggers JRA. It is for this reason it is often called "idiopathic" (no known cause).
Classification systems for JRA vary but may include the following major types:
- Pauciarticular (Oligoarthritis) – about 50% of the cases of JRA are of this type; it affects 4 or fewer joints, usually large joints such as the knees or wrists, and is associated with eye inflammation.
- Polyarticular – affects 5 or more joints, especially those in the fingers and hands; subdivided into two types: rheumatoid factor (RF)-negative and RF-positive; RF-negative is seen more frequently in girls than boys; RF-positive behaves the most like adult rheumatoid arthritis.
- Systemic – least common form of JRA; it affects many parts of the body, including joints and internal organs. Children with this type may have frequent fevers and rashes that can come and go rapidly.
- Psoriatic arthritis – associated with the skin condition psoriasis, either in the child, a sibling, or a parent. Some consider this a separate disease from juvenile chronic arthritis.
- Enthesitis-related arthritis – affects the lower extremities and the spine
- Undifferentiated arthritis – arthritis that does not fit into the above classifications, or fits into more than one
Symptoms may vary from child to child and will frequently change over time, with flare-ups and remissions. In some children, the symptoms may persist; in others, they may permanently disappear. These symptoms may include morning stiffness, limping, reluctance to move an affected joint, joint pain and swelling. Children with systemic JRA may have intermittent fever, rash, swollen lymph nodes and, in some cases, liver, spleen, and (very rarely) lung involvement.
Complications of JRA may include eye inflammation such as uveitis and problems related to joint growth. The disease may cause the affected joints to grow either too quickly or too slowly, causing one arm or leg to be shorter or longer than the other. It may also cause uneven growth in the joint itself. General growth may also be affected by JRA.