ELISA determined IgM and IgA rheumatoid factors in seronegative rheumatoid and psoriatic arthritis.

Previous studies have strongly suggested an association between rheumatoid factors (RF's), particularly IgA-RF, and the presence of erosions in rheumatoid arthritis (RA). The present study was aimed at studying this association in seronegative erosive arthritides. Forty-eight patients with seronegative arthritis were evaluated for the presence of IgM- and IgA-RFs using an enzyme linked immunosorbent assay (ELISA). Twenty-nine had seronegative RA and nineteen had psoriatic arthritis (PA). Twelve (41%) seronegative RA patients were found to be seropositive for IgM- or IgA-RF. Only 1 (7%) patient with PSA was positive for IgA-RF alone. Fifteen (51%) of the RA patients and eight (42%) of the PSA patients had erosive disease. A significant correlation between IgA-RF alone and erosive disease was found only in the seronegative RA patient (p less than 0.02). We conclude that in PSA patients there appears to be no need to define isotype specific RFs. On the other hand, our findings indicate that an early detection of IgA-RF can have clinical importance in seronegative rheumatoid arthritis, as it may constitute an indication for the timely institution of disease-modifying drugs in these patients.