JRA is not a single entity. Rather, it encompasses a group of disorders characterized by chronic noninfectious synovitis and arthritis and is associated with a wide range of systemic manifestations. The hypothetical etiology of the arthritis is that of an autoimmune response to a number of antigens not yet completely identified.
Pauciarticular disease is the most common form of the disease in children. It usually involves a single large joint, typically the knee. Serologic findings for rheumatoid factor are negative, while ANA titers are positive in 90 percent of patients. Extraarticular manifestations of this form of the disease include the development of iridocyclitis, Reiter's syndrome, and inflammatory bowel disease. Ultimate joint damage occurs only infrequently.
Polyarticular disease occurs in approximately a third of cases. Rheumatoid factor (RF) serology may be positive or negative, while ANA titers are positive in 25 percent of the RF-negative patients and 75 percent of RF-positive patients. There is a female preponderance, and both large and small joints may be affected. Contrary to the case in pauciarticular JRA, long-term morbidity with polyarticular disease is related to progressive joint destruction, particularly of the hips and knees.
Systemic JRA is the least common presentation, occurring in only about 20 percent of children with the disease. This form is associated with the particularly high fevers commonly associated with the disease, which characteristically produces one or two fever spikes per day exceeding 39.5°C, and is often associated with shaking chills. In addition, there are other prominent extraarticular manifestations of the disease including a pale, erythematous coalescing macular rash, primarily on the trunk but also present in other areas including palms and soles. Hepatosplenomegaly, pleuritis, and pericarditis are common. Serology for RF and ANA are negative. The arthritis of systemic JRA may progress substantially, leading to joint destruction in as many as a quarter of patients.
Laboratory evaluations associated with the disease are not highly specific for JRA. Arthrocentesis is often necessary to exclude acute suppurative arthritis, particularly in pauciarticular presentations. Initially, radiographs demonstrate only soft tissue swelling and synovial effusions. The findings associated with bone and joint damage occur later.
Emergency department management focuses primarily upon excluding other diagnostic considerations, especially in children who have not previously received a confirmed diagnosis of JRA. Hospital admission is recommended for those children in whom the diagnosis is in doubt or who are to be treated empirically for suspected acute suppurative arthritis while synovial fluid cultures are pending.
Initial therapy for those with an established diagnosis includes aspirin at a dosage of 80 to 125 mg/kg/day, with careful monitoring of salicylate levels to maintain a therapeutic level between 20 and 30 mg/dL. Other nonsteroidal anti-inflammatory drugs are becoming increasingly popular.
The use of glucocorticoids should be reserved for use exclusively in those patients in whom the diagnosis is categorically certain and whose systemic JRA symptoms have proved unresponsive to aspirin. They are also utilized in the management of decompensated pericarditis or myocarditis and in the management of unresponsive iridocyclitis. Other management strategies, including intraarticular glucocorticoid injections and the use of gold or chloroquine, or cytosine, should be initiated by a pediatric rheumatologist.
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