Rheumatoid Factor–Negative Polyarthritis. Approximately 75% of patients with polyarticular-onset arthritis do not have IgM rheumatoid factor in the serum, and the rheumatoid factor test rarely becomes positive 6 months after disease onset. In contrast to rheumatoid factor–positive disease, which primarily affects girls, about 25% of patients in this subgroup are boys.

The arthritis may start at any age, but in about one half of patients onset occurs before age 6. In younger children, parents generally notice only one or two swollen joints, only to have the rheumatologist identify more. The inflammatory process is usually less severe than in rheumatoid factor–positive polyarthritis. Large and small joints are affected, but erosions usually develop later. Early radiographs reveal only osteoporotic changes.

Tenosynovitis on the dorsum of the wrist and tarsus is common, but tenosynovitis in the hand flexors and in tendon structures around the ankle may also be found. Involvement of the finger joints is often symmetric. In young children, swelling of the joints may be partially masked by diffuse swelling of the entire finger (fusiform swelling, see Plate 5-18). Periostitis and widening of the digits are occasionally seen on radiographs. Subcutaneous nodules are uncommon. Chronic, asymptomatic uveitis develops in a small number of patients and is usually associated with a positive ANA test.

The long-term prognosis for patients with rheumatoid factor–negative polyarthritis varies. With treatment, the disease may enter long-term remission, leaving minimal deformities. In others, the course of the disease resembles rheumatoid factor–positive arthritis, only it is less severe. Overall, 70% of children with polyarticular JIA will continue to have some symptoms as adults.

SYSTEMIC-ONSET ARTHRITIS

About 20% of children with juvenile arthritis have the systemic-onset form. The disease may begin at any time during childhood, and both sexes are equally affected. The major signs of systemic-onset juvenile arthritis are a high, spiking fever; characteristic rash; arthritis in one or multiple joints; hepatosplenomegaly; and lymphadenopathy (see Plates 5-16 and 5-17).

The fever in systemic-onset arthritis typically rises above 102°F and falls to normal or below once (quotidian pattern) or twice (double quotidian) during every 24 hours. Although the rise and fall are usually rapid, the pattern of fever may otherwise be quite variable. In some children, the temperature is significantly elevated much of the time, with only short afebrile periods; in others, the duration of the fever spikes is shorter. Single spikes tend to occur in the late afternoon or evening. In patients with a more hectic fever, administration of NSAIDs may change the fever pattern to a once-a-day spike or return the temperature to normal.

The characteristic evanescent rash tends to occur simultaneously with the fever, often disappearing completely during afebrile periods (see Plates 5-16 and 5-17). It may be generalized or develop only in warmer areas such as the axillae and medial thighs or on the palms and soles. The typical rash is macular; individual lesions are pale (“salmon”) pink with relatively indistinct margins and somewhat paler centers. When the rash is extensive, the macules tend to coalesce. About 20% of children with a typical fever pattern have a maculopapular or pruritic rash, and 10% have no rash. In a few children, macules appear along scratch marks made in the skin (Koebner phenomenon). This manifestation, which may not appear immediately, should not be confused with the rapid appearance of the wheal-and-flare response normally seen after scratching.

Severe arthralgia and myalgia are common, particularly during febrile periods. The 30% of children who have no initial evidence of joint involvement may seem to be completely normal during the afebrile periods. During the first 6 months of disease, however, arthritis develops in at least five joints in more than 80% of children with systemic-onset arthritis.

Localized or generalized adenopathy is common; occasionally, the swelling of a single node or groups of nodes is massive, resembling that of cancer. Biopsy findings usually indicate a reactive hyperplasia. Hepatosplenomegaly is also common.