Clinical significance of low molecular weight IgM in patients with systemic lupus erythematosus.

The presence of low molecular weight (LMW) IgM was found in 45% of patients with systemic lupus erythematosus (SLE). Complete chart analysis of clinical and laboratory variables was done on 39 patients with negative LMW IgM (Group 1) and on 40 patients with positive LMW IgM (Group 2). There were statistically significant differences between the 2 groups related to age at onset, hemoglobin concentration, IgM levels, and levels of anti-dsDNA. There were 12 known deaths among the 40 patients in the positive group (30.0%) and only 4 known deaths among the 39 patients in the negative group (10.26%), p less than 0.1. There were no significant intergroup differences of race, sex, mucocutaneous manifestations, arthritis, positive ANA, positive serologic test for syphilis by rapid plasma reagent, Coombs' positive anemia, thrombocytopenia, serositis, incidence of renal and central nervous system involvement. Our study shows that LMW IgM occurred in about half of the patients with SLE. Patients with positive LMW IgM compared to those without it had greater mortality at an earlier age.