Development of selective IgM deficiency in systemic lupus erythematosus patients with disease of long duration.

Statistical analysis of serum immunoglobulin levels in 54 systemic lupus erythematosus (SLE) patients showed a decrease in serum IgM (normal 77 +/- 26 mg/dl; P less than 0.001) that was closely related to disease duration. The longer the duration of SLE, the more striking the decrease in serum levels of IgM (r = -0.74, P less than 0.01). Selective IgM deficiency (less than 47 mg/dl) occurred in SLE patients whose disease was clinically inactive or less active.