Differences between RF negative with RF positive polyarthritis
The RF-negative polyarthritis subgroup includes patients with significant clinical heterogeneity. Two groups of interest within this subgroup include: The clinical features of RF-negative and RF-positive polyarticular JIA are outlined in the below table
Comparison Between Rheumatoid Factor-Negative and -Positive Polyarticular Juvenile Idiopathic Arthritis
| RF-Negative | RF-Positive | |
|---|---|---|
| Peak age of onset (years) | 1–4; 10–12 | >12 |
| Sex ratio, female:male | 3:1 younger; 10:1 older | 4:1 to 13:1 |
| Joint disease | Insidious and progressive Fewer affected joints Asymmetric, larger joints TMJ disease common | More rapid onset Greater number of affected joints Symmetric small joints of hands and fingers (ulnar drift, swan neck, and boutonniere deformities) |
| Serologies | ANA (50%), ACPA (0%–17%) | ANA (55%), ACPA (∼75%) |
| EAMs | Chronic anterior uveitis (15%–20%) | Rheumatoid nodules (30%) Vasculitis, rheumatoid-associated lung disease, Felty syndrome (all rare) |
ACPA , anticitrullinated protein antibodies; ANA , antinuclear antibody; EAMs , extraarticular manifestations; HLA , human leukocyte antigen; RA , rheumatoid arthritis; RF , rheumatoid factor.
• ANA-positive girls aged <7 years: Resemble oligoarticular JIA, except for the fact that the number of joints involved in the first 6 months is more than four. Clinical characteristics include an asymmetric onset of arthritis and higher risk of developing chronic uveitis, similar to that seen in extended oligoarthritis patients.
• ANA-negative children aged >7 to 9 years: Clinical characteristics include a symmetric polyarthritis similar (but not as severe) as RF-positive polyarthritis JIA. These children, as well as children with RF-positive polyarthritis, have an arthritis that is similar to adult RA with both large and small joint involvement. However, they tend to have more hip, shoulder, C-spine, and distal interphalangeal joint involvement than adults. The classic radiographic changes that distinguish these two pediatric groups from adult RA include fusion of the carpal bones, micrognathia, and fusion of the C-spine apophyseal joints.
