(ĐTĐ) - Juvenile rheumatoid arthritis (JRA), also called juvenile idiopathic arthritis (JIA) and juvenile chronic arthritis (JCA), is the most common childhood arthritis. This disease may affect up to 294,000 children in North America alone.

What is juvenile rheumatoid arthritis?

Juvenile rheumatoid arthritis causes joint inflammation and stiffness for more than six weeks in a child aged 16 or younger. Inflammation causes redness, swelling, warmth, and soreness in the joints. Still, many children with JRA do not complain of joint pain.

Any joint can be affected with JRA. The ongoing inflammation may limit the mobility of affected joints.

What causes JRA?

JRA is an autoimmune disorder. This means that the body mistakenly identifies some of its own cells and tissues as foreign. Normally, the immune system fights off harmful, foreign substances such as bacteria or viruses. With JRA, the immune system attacks healthy cells and tissues. The result is inflammation -- marked by redness, heat, pain, and swelling.

Researchers don't know exactly why the immune system goes awry in children with JRA. They suspect that it's a two-step process. First, something in a child's genetic makeup gives them a tendency to develop JRA. Then an environmental factor, such as a virus, triggers the development of JRA.

How is JRA different from adult rheumatoid arthritis?

The main difference between juvenile and adult rheumatoid arthritis is that some people with JRA outgrow the illness. Adults usually have lifelong symptoms. Studies show that by adulthood, JRA symptoms disappear in more than half of all affected children. Another difference between JRA and adult rheumatoid arthritis is the percentage of people who have rheumatoid factor in their blood. The presence of rheumatoid factor indicates an increased chance that JRA will continue into adulthood. About 70% to 80% of adults with rheumatoid arthritis have rheumatoid factor. However, fewer than half of all children with rheumatoid arthritis have rheumatoid factor.

What are symptoms of juvenile rheumatoid arthritis?

JRA may cause chronic fever and anemia. It can affect the heart, lungs, eyes, and nervous system.

These arthritic episodes may last for several weeks. The arthritis flares often recur, but the symptoms may be less severe in recurrent attacks. Symptoms of JRA may include:

  • Repetitive fevers of 103 degrees or higher
  • Pink rash that comes and goes
  • Eye inflammation
  • Joint pain and/or stiffness
  • Limping
  • Joint swelling
  • Reduced activity levels
  • Decreased activity level
  • Weakening of fine motor skills
  • Impaired bone development and growth

Are there different types of juvenile rheumatoid arthritis?

Doctors classify three kinds of JRA. Each type of JRA is based on the number of joints involved, the symptoms, and the presence of certain antibodies in the blood. These three different classifications help determine how the disease will progress.

Pauciarticular JRA

Pauciarticular (paw-see-are-tick-you-lar) means that four or fewer joints are involved. This is the most common form of JRA; about half of all children with JRA have this type.

This type of JRA typically affects large joints, such as the knees. Girls under age 8 are most likely to develop this type of JRA. Some children with pauciarticular JRA have special proteins in the blood called antinuclear antibodies (ANAs).

Eye disease affects from 20% to 30% of children with pauciarticular JRA and is more common in children with ANAs. Regular exams by an ophthalmologist (a doctor specializing in eye diseases) are necessary with JRA.

The ophthalmologist treats serious eye problems such as iritis (inflammation of the iris, the colored part of the eye) or uveitis (inflammation of the inner eye). Many children with pauciarticular disease outgrow JRA by adulthood. Still, eye problems can continue and joint symptoms may recur in some people.

Polyarticular JRA

About 30% of all children with JRA have polyarticular disease, in which five or more joints are affected. The small joints, such as those in the hands and feet, are most commonly involved. However, the disease may also affect large joints.

Polyarticular JRA often is symmetrical. This means it affects the same joints on both sides of the body. Some children with polyarticular disease have rheumatoid factor in their blood. These children often have a more severe form of the disease. Doctors consider this to be the same as adult rheumatoid arthritis.

Systemic JRA

Along with joint swelling, the systemic form of JRA is characterized by fever and a light pink rash. This type of JRA may affect internal organs such as the heart, liver, spleen, and lymph nodes.

The systemic form (called Still's disease) affects 20% of children with JRA. Almost all children with this type of JRA test negative for both rheumatoid factor and ANA.

A small percentage of these children with systemic JRA develop arthritis in many joints. They may have severe arthritis that continues into adulthood.

How is juvenile rheumatoid arthritis diagnosed?

JRA is often difficult to diagnose. Sometimes children with JRA do not complain of pain. In fact, parents may not be aware of symptoms such as swelling.

Some symptoms of JRA are similar to other serious conditions such as infection, cancer, bone disorders, Lyme disease, and lupus.

Physicians usually go through a series of discussions and tests to see if the patient has JRA. During the examination, the physician will review the family medical history to see if there's a possible genetic link. The physician will also review the patient's medical history to see how long the child has had symptoms.

In addition, the physician will do a physical exam to look for joint swelling, rashes, signs of internal organ inflammation, and/ or eye problems. A series of blood tests and joint and tissue fluid tests are also done to check for infection and to confirm the diagnosis.

Lastly, the physician may use X-rays to check for fractures, infections, or tumors. Also, lab tests are done including ANA, rheumatoid factor, HLA-B27 typing, hemoglobin and blood count testing and urinalysis, and erythrocyte sedimentation rate.

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