Chapter 29

### JUVENILE IDIOPATHIC ARTHRITIS

ESSENTIALS OF DIAGNOSIS & TYPICAL FEATURES

• Arthritis, involving pain, swelling, warmth, tenderness, morning stiffness, and/or decreased range of motion of one or more joints, lasting at least 6 weeks.

• May have associated systemic manifestations, including fever, rash, uveitis, serositis, anemia, and fatigue.

Juvenile idiopathic arthritis (JIA) is characterized by chronic arthritis in one or more joints for at least 6 weeks. There are four main subtypes of JIA: (1) oligoarticular, (2) polyarticular, (3) systemic, and (4) enthesitis-associated. The exact cause of JIA is not known, but there is substantial evidence that it is an autoimmune process with genetic susceptibility factors.

#### Clinical Findings

##### A. Symptoms and Signs

The most common type of JIA is the oligoarticular form, which constitutes approximately 30%–40% of patients and is characterized by arthritis of four or fewer joints. This type of JIA often affects medium to large joints. Because the arthritis is often asymmetrical, children may develop a leg-length discrepancy in which the involved leg grows longer due to increased blood flow and growth factors. The synovitis is usually mild and may be painless. Systemic features are uncommon except for inflammation in the eye. Up to 20% of children with this type of JIA develop insidious, asymptomatic uveitis, which may cause blindness if untreated. The activity of the eye disease does not correlate with that of the arthritis. Therefore, routine ophthalmologic screening with slit-lamp examination must be performed at 3-month intervals if the antinuclear antibody (ANA) test is positive, and at 6-month intervals if the ANA test is negative, for at least 4 years after the onset of arthritis, as this is the period of highest risk.

Polyarticular disease is defined as arthritis involving five or more joints. This type of JIA affects 25% of patients. Both large and small joints are involved, typically in a symmetrical pattern. Systemic features are not prominent, although low-grade fever, fatigue, rheumatoid nodules, and anemia may be present. This group is further divided into rheumatoid factor (RF)-positive and RF-negative disease. The former resembles adult rheumatoid arthritis with more chronic, destructive arthritis.

The systemic form, previously known as Still disease, comprises 5%–10% of patients with JIA. The arthritis can involve any number of joints and affects both large and small joints, but may be absent at disease onset. One of the classic features is a high fever, often as high as 39°C–40°C, typically occurring one to two times per day. In between fever spikes, the temperature usually returns to normal or subnormal. Ninety percent of patients have a characteristic evanescent, salmon-pink macular rash that is most prominent on pressure areas and when fever is present. Other systemic features that may be present, but are not specific for JIA, include hepatosplenomegaly, lymphadenopathy, leukocytosis, and serositis.

Enthesitis-associated arthritis is most common in males, older than 10 years of age, and ...

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