The predictive value of fluctuations in IgM and IgG class anti-dsDNA antibodies for relapses in systemic lupus erythematosus. A prospective long-term observation.

OBJECTIVE This study investigated the predictive value of rises in IgM class antibodies against double stranded DNA (anti-dsDNA) for ensuing relapses in systemic lupus erythematosus (SLE) in comparison with rises in IgG class antibodies. In addition, it was analysed whether rises in IgM class anti-dsDNA were associated with specific clinical manifestations of SLE. METHODS Thirty four of a cohort of 72 SLE patients who were positive for IgM class anti-dsDNA at the start of the study or at the time of a relapse were analysed monthly for class specific anti-dsDNA levels during a median observation period of 19.6 months. Disease activity was scored according to the SLE Disease Activity Index. Anti-dsDNA were measured by IgM and IgG class enzyme linked immunosorbent assay (ELISA) and by Farr assay. RESULTS During the study 18 of 34 patients experienced 26 relapses. Twenty two (85%) of the relapses were accompanied by a positive test for IgM class anti-dsDNA by ELISA, 23 (89%) were positive for IgG class anti-dsDNA by ELISA, and 25 (96%) were positive by Farr assay. Patients with rises in IgG class anti-dsDNA by ELISA or in anti-dsDNA by Farr assay had a significantly higher cumulative risk for relapses than patients without those increases (p = 0.04 and p = 0.03, respectively). This was not the case for rises in IgM class anti-dsDNA (p = 0.16). Moreover, a rise in IgM class anti-dsDNA before a relapse was not associated, expressed in terms of odds ratios, with specific clinical manifestations of SLE. CONCLUSION Relapses of SLE are frequently accompanied by IgM class anti-dsDNA. Rises of IgM class anti-dsDNA, in contrast with rises in IgG class anti-dsDNA, are not a sensitive tool for predicting a relapse and are not associated with specific clinical manifestations of SLE.