JRA is arbitrarily defined as beginning before the age of 16 years. Systemic onset JRA does not have a peak age for occurrence in childhood, and appears to effect males and females with equal frequency.
Despite extensive research the cause of this condition remains unclear.
Approximately 20% have acute systemic JRA which is characterized by febrile onset, variable joint manifestations, rash, generalized lymphadenopathy, splenomegaly, liver disease and, rarely, by GI tract disease. Other children with JRA primarily have arthritis that is present at the onset of illness. In 30% only a single joint, usually the knee, is involved; in 50% multiple joints are involved. The disease is termed polyarticular if more than 4 joints are involved and pauciarticular if 4 or fewer joints are affected. The acute systemic onset of JRA is often referred to as Still's disease because of Still's classic description of the disease in 1897.
The systemic symptoms of JRA may precede the onset of overt arthritis for a variable periods of time ranging from months to years. The most characteristic features of systemic JRA are a high-spiking fever and the rheumatoid rash. The temperature peaks once or twice daily, often in the late afternoon or evening, to a level of 39°C or higher with a rapid return to baseline which might be a sub-normal temperature. Chills are frequent at the time of the fever though rigors rarely occur. These children often appear quite ill while febrile but surprisingly well during the rest of the day. These fevers may respond poorly to anti-pyretics (including aspirin). In some instances, the fever responds only to steroid therapy.
The fever in cases of systemic JRA is almost always accompanied by the classic rheumatoid rash. This consists of 2-5mm erythematous morbilliform macules most commonly seen on the trunk and proximal extremities though it may occur on the face, palms, or soles. The rash is non-pruritic but most characteristic is its transient and migratory nature. A single lesion rarely persists for more than an hour. The rash may be seen in a small number of patients with polyarthritis at onset but never with oligoarthritis without other systemic symptoms. The rash can be elicited by rubbing or scratching the skin – Koebner's phenomenon – or may be elicited during a hot bath or with psychological stress.
Children with the systemic onset of JRA usually have lymphadenopathy and hepatosplenomegaly accompanying their active disease. Other organ systems may become involved (i.e. pericarditis or, much less commonly, hepatitis, pulmonary interstitial fibrosis or central nervous system involvement).
The presence of arthritis must be confirmed to make a definite diagnosis of JRA and thus usually occurs within the first year of suspected diagnosis.
Laboratory tests are not helpful in confirming the diagnosis of Still's Disease. Both the ANA and Rheumatoid Factor are usually negative and there is no association with HLA-B27. Antinuclear antibody may be positive, if so, it is often in a speckled pattern. A positive ANA is found in young females with pauciarticular arthritis who are at risk for developing iridocyclitis.
The differential diagnosis includes acute and chronic infection, malignancy, Kawasaki's disease, inflammatory bowel disease, rheumatic fever, and SLE.
About half the children with systemic onset JRA recover nearly completely in time while the other half show progressive involvement of more joints with moderate to severe disability.
Chronic uveitis is a perplexing complication of JRA which occurs most commonly in young girls with oligoarthritis and ANA seropositivity. Around 1/4 of patients with oligoarthritis develop uveitis. In children with chronic uveitis approximately 60% have complete recovery of normal sight, 25% have impaired vision or unilateral blindness, and approximately 10% are blind. Children with systemic JRA rarely develop chronic uveitis (<1%).
Elimination of nightshade family foods may help a small percentage of those with juvenile arthritis.
Aspirin is the preferred drug for therapy given as 80-100mg/kg/day. Higher doses are usually reserved for children with more severe disease. Serum salicylate levels should be maintained between 20 and 30mg/dl. Liver enzymes should be monitored prior to and during aspirin therapy. Some elevation of liver enzymes almost always occurs. Treatment, in the absence of overt side-effects, should be continued for 6 months beyond any indication of active disease and therapy should be tapered slowly. Prednisone in a dose of 1mg/kg/day may be used for brief periods. Physical therapy of the involved joints is essential in preventing long-term disability.
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