Prevalence and concentration of IgM rheumatoid factor in polyarticular onset disease as compared to systemic or pauciarticular onset disease in active juvenile rheumatoid arthritis as measured by ELISA.

The prevalence and concentration of IgM rheumatoid factor (RF) in children with juvenile rheumatoid arthritis (JRA) and its major disease onset groups remains uncertain. In our study enzyme linked immunoabsorbent assay (ELISA) of 68 children with active JRA showed IgM RF in the area of 67% (16/24) of those with polyarticular onset disease, 26% (7/27) of those with systemic onset disease, and 6% (1/17) of those with pauciarticular onset disease. The median IgM RF concentration was 50-fold higher in polyarticular disease compared to systemic disease. The prevalence of IgM RF in polyarticular disease was greater in those with severe disease (functional classes and 3 and 4), with 90% (9/10) seropositive. By agglutination assay, the prevalence of IgM RF in JRA was significantly less than by ELISA, with 33% of the polyarticular group positive for IgM RF, and none of the systemic group positive, Relatively low concentration IgM RF similar to that seen in systemic JRA was also found in high prevalence in the area of children with non-JRA, systemic rheumatic disease (n = 8). In summary, our study shows by ELISA that high concentrations of IgM RF are found essentially only in the sera of children with polyarticular onset JRA and especially in those with severe disease.

High prevalence of IgA rheumatoid factor in severe polyarticular-onset juvenile rheumatoid arthritis, but not in systemic-onset or pauciarticular-onset disease.

The presence of IgA rheumatoid factor (IgA-RF) has been correlated with severe joint disease in adult rheumatoid arthritis (RA), but IgA-RF has not been reported in juvenile rheumatoid arthritis (JRA). In the present study, IgA-RF was assayed by an enzyme-linked immunosorbent assay and was found in the sera of 14 of 24 children (58%) with active polyarticular JRA. The presence of IgA-RF correlated with the degree of functional disability. In contrast, IgA-RF was not found in the sera of systemic-onset disease patients, regardless of the degree of dysfunction. IgA-RF was detected in only 1 patient with pauciarticular disease, despite the fact that several patients in this group had severe disease. The presence of IgA-RF in polyarticular JRA did not correlate with serum IgA levels, but did correlate with the presence and the level of serum IgM-RF. Thus, the presence of IgA-RF appears to be specific for polyarticular JRA, and shows a correlation with severe disease in this group.