In 2004, major changes were made to the classification of children with JIA. Based on expert consensus, children with JIA were subclassified into seven subtypes: oligoarticular (either persistent or extended), rheumatoid factor–negative polyarticular, rheumatoid factor–positive polyarticular; systemic arthritis, enthesitis-related arthritis, psoriatic arthritis, and undifferentiated arthritis. Although these subcategories are useful in identifying populations for clinical trials, it is likely that they represent unique conditions that share arthritis as a cardinal feature.

OLIGOARTICULAR ARTHRITIS

Oligoarticular arthritis occurs in 55% to 60% of children with juvenile arthritis. The arthritis is limited to fewer than five joints during the first 6 months after diagnosis. Those patients whose arthritis remains confined to four or fewer joints 6 months after diagnosis are classified as having persistent oligoarticular JIA. Some children may develop involvement of five or more joints after the initial 6-month period and are classified as having extended oligoarticular JIA. In patients whose arthritis extends beyond a few joints, the disease resembles rheumatoid factor–negative polyarthritis and produces more dysfunction than was predicted from the original, limited involvement. Disease activity may be intermittent and even recur in previously uninvolved joints, even after years of remission.

Oligoarticular disease is most likely to be found in toddlers and in females more frequently than males. It is rare for these children to complain about pain; medical care is typically a result of parental observation of joint swelling or the onset of a new functional disability. The knee is most often affected in oligoarticularonset disease, and monarticular involvement is common. When the knee is involved, parents will often report their child limps in the morning or wishes to be carried. The ankles are the next most common site of involvement, followed by the wrists, elbows, and hips. The small joints of the hands and feet, the cervical spine, and the jaw are affected less often than in polyarticularonset arthritis.

In some children, the joint contains only a small amount of fluid, particularly in the early stages. The bulge sign is used to confirm the presence of small amounts of fluid in the knee (see Plate 5-19). The bulge is elicited by compressing or stroking proximally the medial side of the knee, moving fluid into the suprapatellar bursa and the lateral compartment. Rapid compression of the lateral compartment moves fluid back to the medial side, resulting in a bulging of the medial compartment. The effusion may also be demonstrated by compressing the suprapatellar bursa or by distally stroking the lateral compartment. Other important physical examination findings include muscle atrophy or joint contractures.

In monarticular disease, overgrowth of the involved limb may occur as a result of increased blood supply to the immature growth plate; this is seen most frequently with arthritis of one knee. With remission or treatment, overgrowth ceases, allowing growth in the uninvolved limb to catch up. If left untreated, persistent inflammation results in premature closure of the growth plate and shortening of the affected limb. If the lim-blength discrepancy is predicted to be greater than 2.5 cm, early epiphyseal stapling or epiphysiodesis of the affected side may be indicated.

Uveitis in Juvenile Idiopathic Arthritis. A potentially blinding yet clinically silent uveitis is most likely to develop in children with oligoarticular JIA. Only 5% of children with the polyarticular subtype will develop uveitis compared with approximately 20% of children with oligoarticular JIA. This ocular inflammation usually begins within 2 years of the onset of arthritis, and nearly always within the first 4 years. In some children, uveitis becomes evident before the joint manifestations and it is typical for the inflammatory activity in the joints and eyes to occur independent of each other. Patients most at risk for uveitis are girls who are younger than 6 years of age at the onset of arthritis with the oligoarticular subtype, a positive antinuclear antibody (ANA) test, and disease duration of less than 4 years. Periodic slit lamp examination is used to detect ocular inflammation in the early stage and is mandatory in all children with juvenile arthritis. The early changes are not seen readily with the ophthalmoscope.