Material provided by the National Institute of Arthritis and Musculoskeletal and Skin Diseases. You may visit their website at www.nih.com.

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The American College of Rheumatology has 3 classifcations for juvenile idiopathic arthritis. The classifications are done by the number of joints involved, the symptoms, and the presence or absence of certain antibodies in the blood. (Antibodies are special proteins made by the immune system.) These ACR classifications help the doctor determine how the disease will progress.

• Pauciarticular: Pauciarticular (paw-see-are-tick-you-lar) means that 4 or fewer joints are affected. Pauciarticular is the most common form of JIA; about half of all children with JIA 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 JIA.
  
  Some children have special proteins in the blood called antinuclear antibodies (ANAs). Eye disease affects about 20 to 30% of children with pauciarticular JIA. Up to 80% 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) or uveitis (inflammation of the inner eye, or uvea).
  
  Many children with pauciarticular disease outgrow arthritis by adulthood, although eye problems can continue and joint symptoms may recur in some people.

• Polyarticular: About 30% of all children with JIA have polyarticular disease. In polyarticular disease, 5 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 JIA often is symmetrical; that is, it affects the same joint on both sides of the body.
  
  Some children with polyarticular disease have a special kind of 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 the same as adult rheumatoid arthritis.

• Systemic: Besides joint swelling, the systemic form of JIA (which you may hear called systemic juvenile idiopathic arthritis, or SJIA) is characterized by fever and a light pink 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 JIA test negative for both RF and ANA. The systemic form affects 20% of all children with JIA. A small percentage of these children develop arthritis in many joints and can have severe arthritis that continues into adulthood.

A group in Europe, the European League Against Rheumatism (or EULAR), has slightly different classifications.  They have suggested the name juvenile chronic arthritis (as compared to the ACR name juvenile idiopathic arthritis) for the general name of the disorder.

The main difference between the ACR and the EULAR criteria is that EULAR includes subtypes based on the presence or absence of the rheumatoid factor (RF).  For example, they have a type "polyarticular juvenile arthritis-rheumatoid factor positive," as well as a "polyarticular juvenile idiopathic arthritis-rheumatoid factor negative."

The EULAR critieria for juvenile chronic arthritis (or juvenile idiopathic arthritis) also includes juvenile ankylosing spondylitis and juvenile psoriatic arthritis.

Note: Juvenile idiopathic arthritis (JIA) was previously known as Juvenile rheumatoid arthritis (JRA).