Specificity of granular IgM deposition in folliculosebaceous units and sweat gland apparatus in direct immunofluorescence (DIF) of lupus erythematosus

Abstract

Diagnosis of lupus erythematosus (LE) in direct immunofluorescence testing is based on the finding of positive immunofluorescence at the dermoepidermal junction (DEJ). We sought to evaluate the sensitivity of IgM deposition at the DEJ and adnexal structures in the diagnosis of lupus erythematosus. We conducted a retrospective study of 100 previously diagnosed cases of lupus erythematosus and 158 cases of other immune-mediated dermatosis. Deposition of IgG, IgM, IgA, and C3 at the DEJ, follicular units, and sweat glands were recorded. Presence or absence of adnexal structures was documented. The immunoreactant deposition was documented as linear, coarse granular, or stippled. The most frequently deposited immunoreactant in lupus erythematosus cases was IgM along the DEJ and stromal-epithelial junction of hair follicles and sweat glands. IgM deposition along the stromal-epithelial junction of hair follicles and sweat glands was strongly associated with a diagnosis of lupus erythematosus compared with other immune-mediated diseases collectively (P value<.001). The pattern of IgM in lupus and dermatomyositis is granular, in contrast to the linear deposition in the other disorders evaluated. This was a retrospective study of archived material. Granular IgM deposition at the stromal-epithelial junction of cutaneous adnexal structuressuggests a diagnosis of lupus erythematosus or dermatomyositis.