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JUVENILE IDIOPATHIC ARTHRITIS

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Juvenile idiopathic arthritis (JIA; juvenile rheumatoid arthritis) encompasses a group of disorders that are clinically characterized by a chronic synovitis of unknown origin that begins when the patient is less than 16 years of age, and persists for more than 6 weeks. Subgroups of JIA include pauciarticular (4 or fewer joints involved), polyarticular (5 or more joints), and systemic-onset varieties. Synovial inflammation in these patients stimulates synovial proliferation and joint effusion. Pannus formation in the synovium can lead to erosion of cartilage and bone.1

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Pauciarticular Juvenile Idiopathic Arthritis

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Pauciarticular arthritis is the most common form of JIA. These patients have involvement of 4 or fewer joints during the first 6 months of clinical disease; additional joints may become involved subsequently. The major areas of involvement include the knee, ankle, elbow, and wrist. The distribution is often asymmetric. There are 2 subtypes of pauciarticular disease.

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Pauciarticular JIA type I accounts for approximately 35% to 40% of patients with JIA. Approximately 80% of these patients are girls. The clinical onset is usually prior to the age of 4 or 5 years. Many patients with this subtype are seronegative for rheumatoid factor, but 90% have positive tests for antinuclear antibodies. The hips and sacroiliac joints are not affected in these patients. About one-quarter of children with pauciarticular disease have iridocyclitis or anterior uveitis.

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Pauciarticular disease type II involves approximately 10% to 15% of children with JIA. This is predominantly a disease of boys, with a clinical onset that is usually after the age of 8 years. Serological tests for rheumatoid factor and antinuclear antibodies are usually negative; approximately 75% of these patients have the histocompatibility antigen HLA-B27. This disorder predominantly involves large joints; the hips and sacroiliac joints are usually affected. Some patients develop manifestations of ankylosing spondylitis.

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Polyarticular Juvenile Idiopathic Arthritis

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Polyarticular JIA is characterized by involvement of multiple joints (i.e., 5 or more). There are 2 major subtypes of polyarticular disease: rheumatoid factor–negative polyarthritis, which accounts for 20% to 25% of cases of JIA, and rheumatoid factor–positive polyarthritis, which accounts for 5% to 20% of cases. Girls are affected more frequently than boys with both subtypes of polyarticular JIA.

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Rheumatoid factor–negative polyarticular arthritis may present at any time during childhood. The clinical course is relatively mild, although up to 15% of these patients have severe clinical manifestations. Rheumatoid nodules are rare with this form of polyarthritis. Both large and small joints are usually involved, often with a symmetric distribution. The onset of the rheumatoid factor–positive polyarticular disease is most often late during childhood. There is a frequent association with the HLA DR4 histocompatibility antigen. About half of these patients have a clinically severe form of arthritis. Subcutaneous rheumatoid nodules are common.

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Children with polyarticular JIA may experience an insidious onset, with joint stiffness, swelling, ...

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