Polyarticular juvenile idiopathic arthritis (JIA), also known as polyarthritis, affects 5 or more joints during the first 6 months of symptoms. This type of JIA is more severe than oligoarticular JIA, because it affects more joints and tends to get worse over time.

Polyarticular JIA often begins in large joints, such as the knee or hip, but may start in the small joints of the hands and fingers. It also may affect the knees, ankles, feet, neck, and jaw.

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).

Symptoms of polyarticular JIA usually affect the same joints on both sides of the body, such as the joints of both hands. A child with polyarthritis may also develop:

• Joint damage (erosion).
• Whole-body (systemic) symptoms, such as weakness, fever, and rash.
• Small bumps under the skin (rheumatoid nodules), especially at pressure points such as the elbows or heels. This is most common in RF-positive polyarthritis.