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.