A small subgroup of patients (approximately 10%) with juvenile arthritis does not present with onset of arthritis but rather with preceding systemic inflammation. This form of JIA, thought to be an autoinflammatory disease, manifests with a typical recurring, spiking fever, usually once or twice per day, which can occur for several weeks to months. This is accompanied by a rash, typically morbilliform and salmon-colored. The rash may be evanescent and occur at times of high fever only. Rarely the rash can be urticarial in nature. Internal organ involvement also occurs. Serositis, such as pleuritis and pericarditis, occurs in 50% of children. Pericardial tamponade rarely may occur. Hepatosplenomegaly occurs in 70% of children. Children with systemic-onset JIA appear sick; they have significant constitutional symptoms, including malaise and failure to thrive. Laboratory findings show the inflammation, with elevated erythrocyte sedimentation rate, C-reactive protein, white blood cell count, and platelet counts and anemia. The arthritis of JIA follows the systemic inflammation by 6 weeks to 6 months. The arthritis is typically polyarticular in nature and can be extensive and resistant to treatment, placing these children at highest risk for long-term disability.
The spondyloarthropathies describe a group of arthritides that include inflammation of the axial skeleton and sacroiliac joints and enthesitis, or inflammation of tendinous insertions. These include juvenile ankylosing spondylitis, psoriatic arthritis, and the arthritis of inflammatory bowel disease. This group of diseases can also present with peripheral arthritis and can be initially classified in other subgroups. It is only later, when the patient develops evidence of sacroiliac arthritis, psoriasis, or gastrointestinal disease, that the diagnosis becomes clear (Table 89-2). Other important features of this group include the frequent presence of HLA-B27 and the need for earlier treatment with tumor necrosis factor (TNF) blockers.
Most children with oligoarticular JIA have no laboratory abnormalities. Children with polyarticular and systemic-onset disease commonly show elevated acute phase reactants and anemia of chronic disease. In all pediatric patients with joint or bone pain, a complete blood count should be performed to exclude leukemia, which also can present with limb pain (see Chapter 155). All patients with oligoarticular JIA should have an antinuclear antibody test to help identify those at higher risk for uveitis. Older children and adolescents with polyarticular disease should have a rheumatoid factor performed to identify children with early onset adult rheumatoid arthritis.
Diagnostic arthrocentesis may be necessary to exclude suppurative arthritis in children who present with acute onset of monarticular symptoms. The synovial fluid white blood cell count is typically less than 50,000 to 100,000/mm3 and should be predominantly lymphocytes, rather than neutrophils seen with suppurative arthritis. Gram stain and culture should be negative (see Chapter 118).
The most common radiologic finding in the early stagesof JIA is a normal bone x-ray. Over time, periarticular osteopenia, resulting from decreased mineralization, is mostcommonly found. Growth centers may be slow to develop,whereas there may be accelerated maturation of growth platesor evidence of bony proliferation. Erosions of bony articularsurfaces may be a late finding. If the cervical spine is involved,fusion of C1-4 may occur, and atlantoaxial subluxation maybe demonstrable.