What Is Arthritis?

Arthritis means "joint inflammation" and refers to a group of diseases that cause pain, swelling, stiffness, and loss of motion in the joints. "Arthritis" is often used as a more general term to refer to the more than 100 rheumatic diseases that may affect the joints but can also cause pain, swelling, and stiffness in other supporting structures of the body such as muscles, tendons, ligaments, and bones. Some rheumatic diseases can affect other parts of the body, including various internal organs. Children can develop almost all types of arthritis that affect adults, but the most common type that affects children is juvenile rheumatoid arthritis (JRA).

What Is Juvenile Rheumatoid Arthritis?

Juvenile rheumatoid arthritis is arthritis that causes joint inflammation and stiffness for more than 6 weeks in a child of 16 years of age or less. Inflammation causes redness, swelling, warmth, and soreness in the joints, although many children with JRA do not complain of joint pain. Any joint can be affected and inflammation may limit the mobility of affected joints. One type of JRA can also affect the internal organs. Doctors classify JRA into three types by the number of joints involved, the symptoms, and the presence or absence of certain antibodies found by a blood test. (Antibodies are special proteins made by the immune system.) These classifications help the doctor determine how the disease will progress and whether the internal organs or skin is affected.

Pauciarticular (PAW-see-are-TICK-you-lar)

Pauciarticular means that four or fewer joints are affected. Pauciarticular is the most common form of JRA; about half of all children with JRA have this type. Pauciarticular disease typically affects large joints, such as the knees. Girls under age 8 are most likely to develop this type of JRA.

Some children have special kinds of antibodies in the blood. One is called antinuclear antibody (ANA) and one is called rheumatoid factor. Eye disease affects about 20 to 30 percent of children with pauciarticular JRA. Up to 80 percent of those with eye disease also test positive for ANA and the disease tends to develop at a particularly early age in these children. Regular examinations by an ophthalmologist (a doctor who specializes in eye diseases) are necessary to prevent serious eye problems such as iritis (inflammation of the iris, the colored part of the eye) or uveitis (inflammation of the uvea, or the inner eye). Some children with pauciarticular disease outgrow arthritis by adulthood, although eye problems can continue and joint symptoms may recur in some people.

Polyarticular

About 30 percent of all children with JRA have polyarticular disease. In polyarticular disease, five or more joints are affected. The small joints, such as those in the hands and feet, are most commonly involved, but the disease may also affect large joints. Polyarticular JRA often is symmetrical; that is, it affects the same joint on both sides of the body. Some children with polyarticular disease have an antibody in their blood called IgM rheumatoid factor (RF). These children often have a more severe form of the disease, which doctors consider to be similar in many ways to adult rheumatoid arthritis.

Systemic

Besides joint swelling, the systemic form of JRA is characterized by fever and a light skin rash, and may also affect internal organs such as the heart, liver, spleen, and lymph nodes. Doctors sometimes call it Still's disease. Almost all children with this type of JRA test negative for both RF and ANA. The systemic form affects 20 percent of all children with JRA. A small percentage of these children develop arthritis in many joints and can have severe arthritis that continues into adulthood.