Immunoglobulin M predominance in cutaneous lupus erythematosus

Direct immunofluorescence (DIF) is a valuable tool in the diagnosis of cutaneous lupus erythematosus (LE). Our goal was to characterize the most frequent immune reactants in the skin biopsies of cutaneous LE and identify the most common immunofluorescence staining patterns.

DIF results of immunoglobulin G (IgG), IgA, IgM, C3, and fibrinogen from 199 patients between 1989 and 1998 were retrospectively analyzed. Confirmatory clinical and serological diagnosis of LE subtype was available for 95 patients. Intensity of staining was ranked from 0 to 4+ but only included as significant if >/=2+. Laboratory values were gathered and analyzed for all patients who had distinct granular immune deposition for Ig and/or complement.

The most commonly detected individual Ig was IgM in 149 (75%) specimens. IgM and C3 combination was the most common pair expressed with 98 (49%) specimens. The most common triplet was IgM, C3, and fibrinogen in 63 (32%) specimens. The most common quadruplet was the combination of IgG, IgM, C3, and fibrinogen in 42 (21%) specimens. All the five immunoreactants were detected in only 25 (13%) specimens. Systemic LE patients had a higher percent of abnormal laboratory values compared to discoid LE (DLE) and subacute LE (SCLE) patients (p = 0.02). Fibrinogen staining was found to be significantly higher in DLE patients and lowest in SCLE patients (p = 0.05).

This study demonstrates a marked predominance of IgM +/- C3 in cutaneous LE. When used in conjunction with other data, DIF is an extremely powerful tool in the routine evaluation of the LE patient. Our report emphasizes the importance of IgM expression in the diagnosis of LE by DIF and how positive staining with multiple conjugates can raise its sensitivity.