POLYARTICULAR-ONSET ARTHRITIS

About 20% to 25% of children with juvenile arthritis exhibit polyarticular onset, which is characterized by involvement of five or more joints and the absence of significant systemic manifestations. High serum levels of IgM rheumatoid factor are found in 25% of patients with polyarticular-onset arthritis. This finding led to the classification of polyarticular-onset arthritis into two distinct types: rheumatoid factor–positive and rheumatoid factor–negative.

Polyarticular-onset arthritis affects both large and small joints, including the cervical spine, temporomandibular joints, and growth centers of the mandible. The distribution is generally symmetric.

Radiographs of the involved cervical spine initially reveal a loss of the normal curve; with time, the apophyseal joints (most often at C2 to C3) may narrow and eventually fuse (see Plate 5-21). The fusion may affect the whole cervical spine or only segments. Because limitation of motion is most significant in extension and lateral motion, some children hold the head in a position of fixed flexion (see Plate 5-21). Anterior subluxation of C1 on C2 is a potentially serious complication seen with extensive fusion below C2.

Arthritis of the cervical spine is associated with involvement of the temporomandibular joints, which may result in poor growth of the mandible and crowding of the teeth. Children may refuse to eat breakfast owing to pain and stiffness in this joint, but 80% of children with temporomandibular joint arthritis are asymptomatic. Growth of the maxilla is rarely affected. If temporomandibular joint involvement is unilateral, the lower jaw shifts significantly to the affected side when the mouth is opened. Limitation of intraincisal distance is also a common finding.

In the hands and feet, the arthritis affects multiple joints in a symmetric pattern. Attenuation of supporting structures and damage to tendons, tendon sheaths, and attachments lead to joint laxity and subluxation. The metacarpophalangeal and proximal interphalangeal joints of the hands are affected first, followed by the distal interphalangeal joints (see Plate 5-18).

Rheumatoid Factor–Positive Polyarthritis. This juvenile version of adult rheumatoid arthritis usually develops in girls older than 10 years of age. The arthritis, which involves multiple large and small joints, is erosive, aggressive, and chronic. Erosions in the small joints may be evident radiographically as early as 6 months after onset of disease, and the destructive synovitis may continue for 10 years or longer.

Subcutaneous rheumatoid nodules may occur, usually developing at or distal to the elbow on the extensor surface. Constitutional manifestations of rheumatoid factor–positive polyarthritis include low-grade fever, easy fatigability, mild-to-moderate anemia, and poor weight gain. Uveitis (iridocyclitis) and episcleritis are rare.