Rheumatoid Arthritis Health Center

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Polyarticular JIA (polyarthritis) affects 5 or more joints in the first 6 months of the disease-often the knee, hip, wrist, elbow, and ankle joints-and may affect the small joints in the hands and feet. This type of JIA is more severe than most cases of oligoarticular JIA because it affects more joints and tends to get worse over time. Joint damage can be seen on X-ray within 2 years in children with more severe disease. About 30% of children affected by JIA have the polyarticular form.⁴ Of these children, many will have active disease that continues into adulthood.

Polyarticular JIA is divided into two groups.

• If an antibody called rheumatoid factor is present in the blood, the polyarthritis is rheumatoid factor-positive (RF-positive).
• If the rheumatoid factor antibody is not present, the polyarthritis is rheumatoid factor-negative (RF-negative).

Of all children with juvenile idiopathic arthritis, fewer than 10% have RF-positive polyarticular JIA.⁴ Normally, antibodies are produced by the immune system to help destroy and eliminate invading bacteria and viruses that can cause disease. But RF is an antibody that can attach to normal body tissue, resulting in damage. RF-positive polyarticular JIA is thought to be identical to adult rheumatoid arthritis. The risk of joint deformity is highest (about 50% likelihood) in children with RF-positive polyarticular JIA.⁵ In RF-positive JIA:

• Some children develop bumps under the skin (rheumatoid nodules) over pressure points (such as the elbow or back of the heel).
• Children are less likely to have a long-term remission of symptoms, so they have a higher risk of disability as an adult.

RF-negative JIA is much more common than RF-positive JIA. In RF-negative JIA:

• Joints of the jaw and neck may be affected.
• There is an increased risk of inflammatory eye disease.
• About 1 in 3 children go into long-term remission.

Systemic JIA

About 10% of children affected by JIA have the systemic form.⁴ Usually, a child who has systemic JIA will have fever spikes and a rash for weeks to months before arthritis joint pain begins. Whole-body (systemic) symptoms (such as fatigue and loss of appetite) and enlarged lymph nodes, liver, and spleen may come and go during the first years of the disease. Some children with systemic JIA develop heart and complications.⁵

Some children with systemic JIA will have joint damage visible on X-ray within 2 years. Many will continue to have active disease as adults. While some children have one course of this disease that lasts 2 to 4 years, others continue to have mild joint pain and flares of other symptoms. A few have ongoing destructive arthritis, often into adulthood, even with treatment.⁴

Enthesitis-related JIA

About 10% of children with JIA have the enthesitis-related form. An enthesis is the area where a tendon or ligament attaches to a bone. In enthesitis-related JIA, that area is inflamed and tender. This is most common in the front of the knee and at the heel. In addition to enthesitis, the child has joint pain and inflammation (arthritis), or 2 or more other features such as:⁴

• Sacroiliac tenderness (where the spine meets the pelvis).
• Low back and buttock pain and inflammation.
• Presence of an antigen called HLA-B27 in the blood.
• Inflammatory eye disease.
• Family history of another condition related to HLA-B27, such as ankylosing spondylitis.