The histocompatibility of human leukocyte antigen B27 (HLA-B27) is detected in a large percentage of patients in this subgroup. Children should not be included in this subgroup solely because of the presence of HLA-B27, which is also found in children with other types of juvenile arthritis at the same frequency as in the general population.

DIFFERENTIAL DIAGNOSIS

Systemic-onset arthritis may resemble a number of other diseases. When joint inflammation is absent, it may be confused with infectious, oncologic, or inflammatory diseases. When joint inflammation is present, infectious arthritis, osteomyelitis, and malignancy, especially leukemia, must be ruled out. Other diagnostic possibilities include a variety of systemic autoimmune diseases including lupus, inflammatory bowel disease, various types of systemic vasculitis, and, occasionally, reactions to infections or drugs.

Polyarticular arthritis must be differentiated from other joint diseases such as systemic lupus erythematosus and acute rheumatic fever. Unlike these conditions, however, polyarticular arthritis rarely has significant systemic manifestations.

Oligoarticular-onset arthritis, especially monarticular involvement, can be confused with trauma, joint conditions such as osteochondritis, viral-induced synovitis, Lyme disease, hemarthrosis, vascular malformation, and benign soft tissue tumors such as pigmented villonodular synovitis.

Laboratory studies have no role in the diagnosis of JIA; JIA is a clinical diagnosis, and laboratory studies only aid in the subcategorization of children with arthritis. Up to 30% of the general pediatric population may have a positive ANA, compared with approximately 50% of children with JIA. ANA testing is performed in the diagnostic evaluation of children with JIA only to properly assess their risk for uveitis. Similarly, 3% of healthy children may have serologic evidence of IgM rheumatoid factor whereas up to 10% of patients with JIA manifest similar results. All patients diagnosed with JIA should undergo testing for rheumatoid factor to assist with proper subclassification, but a negative rheumatoid factor test does not rule out JIA. In addition, serologic testing should also include assessment of anti-CCP antibody, an IgG antibody that portends an aggressive and destructive disease course similar to rheumatoid factor–positive disease. Children with JIA may have evidence of systemic inflammation with an elevated ESR, anemia, and thrombocytosis, yet these tests are frequently normal at the time of diagnosis in most patients with JIA.

Although a promising area of research, genetic sequencing is of little clinical value at present. There is a significantly increased frequency of HLA-B27 in older males with enthesitis-related arthritis and an increased frequency of HLA-DR4 in children with rheumatoid factor–positive polyarthritis, similar to that seen in adult rheumatoid arthritis. Similarly, HLA-DR5 and HLA-DRw8 are often found in patients with oligoarticular-onset arthritis and in those with rheumatoid factor–negative polyarthritis. However, because the same markers are present in many normal people, their demonstration is of value only in population studies, not in individual patients.

TREATMENT

The treatment of juvenile arthritis is multifaceted, requiring a coordinated team approach. Ideally, the primary care physician, rheumatologist, orthopedist, pedodontist, ophthalmologist, and physical therapist should all be involved in the treatment program.