Juvenile rheumatoid arthritis (JRA), also known as “juvenile chronic polyarthritis,” or “Still’s disease,” is the most common disorder of childhood involving chronic joint inflammation (synovitis). Since there is a spectrum of signs and symptoms, diagnosis partially depends on exclusion of other recognized arthritis syndromes (some of which are discussed later). There are three subdivisions of JRA. Polyarticular JRA accounts for 40%-50% of all JRA cases and produces inflammation of multiple joints (more than four), typically in a symmetric distribution. There is no eye involvement, and those affected are predominantly girls. There are two subgroups. In one subgroup, accounting for about 10% of JRA cases, the RA test result is positive, and there is a high incidence of positive antinuclear antibody (ANA) test results. This form occurs more often in late childhood and frequently is associated with severe arthritis; it more closely resembles standard adult RA. The other subgroup accounts for about 30% of JRA cases. RA test results are negative, there is a low incidence of positive ANA test results, and severe arthritis is rare. This form of JRA resembles minimal severity adult RA. Polyarticular JRA frequently is associated with a mild normocytic-normochromic anemia. WBC counts are normal or mildly elevated, usually not more than 20,000/mm3 (20 Ч 109/L).

Pauciarticular JRA accounts for 30%-40% of all JRA cases and affects only a few joints (less than four) in asymmetric distribution. There are also two subgroups (although this is disputed). The early-onset type occurs before age 5 years and accounts for about 30% of JRA cases. There is no hip or spine involvement, but about one half of affected patients develop iridocyclitis. RA test results are negative, but ANA test results are positive in about 50% of patients. The late-onset subgroup overlaps with ankylosing spondylitis and is not included in JRA by some investigators. This form affects predominantly boys. Hip and sacroiliac involvement are frequent but not iridocyclitis. There is a high incidence of the HLA-B27 antigen, and RA or ANA test results are usually negative.

Systemic-onset JRA accounts for approximately 20% of JRA cases. Slightly more boys are affected than girls, and onset can occur at any age. There are one or two high fever spikes each day, especially in the evening, for several weeks, with the temperature rapidly dropping after each spike to normal or even low values. There may be chills at the same time as the fever spikes. Some 90% or more of patients develop a macular skin rash that often appears and disappears with the fever spikes. There is splenomegaly or lymphadenopathy in 80%-85% of cases, pleuritis or pericarditis in 30%-60%, and abdominal pain in 30%. Anemia is frequent and may sometimes be severe. Leukocytosis is found in 95%, and WBC counts are often in the range of 20,000-30,000/mm3. Eventually a polyarthritis develops. RA and ANA test results are negative.