IgM, IgA, and IgG rheumatoid factors in early rheumatoid arthritis predictive of radiological progression?

The significance of IgM, IgA and IgG rheumatoid factors (RF) for the prediction of radiological progression, and as process variables during follow-up, was evaluated in a three-year prospective study of 149 patients with early rheumatoid arthritis (symptoms < 1 year at study entry). The occurrence of IgA-RF and IgG-RF at study entry without simultaneous occurrence of IgM-RF, and the seroconversion from RF-negative at entry to RF-positive during follow-up appeared to be unusual. A significant correlation was found between each of the RF-isotype levels at entry and radiological progression after three years. However, no significant prognostic value of IgA-RF and IgG-RF could be demonstrated if analysed in combination with IgM-RF, initial disease activity (as measured by C-reactive protein level), initial radiologic score, HLA-DR4 and HLA-DR2. Although IgM-RF levels generally reflected the course of disease activity and did so better than IgA-RF and IgG-RF levels, their clinical significance as process variables appeared to be limited compared to C-reactive protein.