Arthritis: Juvenile Rheumatoid Arthritis (JRA)

Juvenile rheumatoid arthritis (JRA) is the most common type of arthritis affecting children. Rheumatoid arthritis is a chronic (long-lasting) disease that can affect joints in any part of the body. JRA is defined as an arthritis that causes joint inflammation and stiffness for more than 6 weeks in a child less than 16 years of age.

In this disease, the immune system mistakenly targets the tissue that lines the inside of the joint, called the synovium. The synovium responds by making excess fluid (synovial fluid), which leads to swelling, pain and stiffness. The inflammation can then spread to the surrounding tissues, eventually damaging cartilage and bone. Other areas of the body -- including the eyes, kidneys, lungs and heart -- also may be affected by the inflammation. Without treatment, JRA can interfere with a child's normal growth and development.

There are three main subtypes of JRA, which are based on symptoms and the number of joints involved.

• Systemic JRA. Also called Still's disease, this type occurs in about 20% of children with JRA. A systemic illness is one that can affect the entire person or all body systems. Systemic JRA usually causes a high fever and a rash, which most often appears on the torso, arms and legs. It also can affect internal organs, such as the heart, liver, spleen and lymph nodes. This type of JRA affects boys and girls equally.
• Pauciarticular. This type of JRA affects fewer than five joints, most often the knee and wrist joints. Often only one knee is affected. It also can cause inflammation of the iris (the colored area of the eye), called iridocyclitis or iritis. About half of all children with JRA have this type, and it is more common in girls than in boys. Most children will outgrow this type of arthritis by adulthood.
• Polyarticular. This type of JRA affects five or more joints, usually the same ones on each side of the body. Polyarticular JRA most often affects small joints, such as those in the hands and feet. It is more common in girls than in boys

What Are the Symptoms of JRA?

Symptoms may vary depending on the type of JRA and may include:

• Morning stiffness
• Pain, swelling and tenderness in the joints
• Fever
• Rash
• Weight loss
• Fatigue or irritability
• Eye inflammation

What Causes JRA?

The exact cause of JRA is not known. However, researchers are studying several factors that may be involved, alone or in combination, to trigger the inflammatory reaction seen in JRA. These factors include genetics (heredity), infection and other environmental factors that impact the immune system.

How Common Is JRA?

JRA is the most common type of arthritis in children. It affects about 100,000 children in the United States.