Abstract

            The diagnostic utility of immunhistochemical (IHC) staining on paraffin sections in bullous disorders is useful when frozen tissue is not available. In pemphigus vulgaris (PV) and pemphigus foliaceus (PF), an intercellular lace-like staining pattern of IgG4 has been described, with a similar sensitivity and specificity to direct immunofluorescence (DIF). We observed intercellular IgG4 reactivity in a few acantholytic conditions other than PV and PF. Here, we identified two cases of Grover’s disease, one case of IgA pemphigus and one case of Sneddon Wilkinson disease that demonstrate intercellular IgG4 staining in keratinocytes. The diagnosis of both IgA pemphigus and Sneddon Wilkinson disease were confirmed by DIF studies. In terms of IHC staining, IgG4 reactivity was focal toward the edge of the lesion for the two Grover’s disease. In the cases of IgA pemphigus and Sneddon Wilkinson, a diffuse intercellular IgG4 staining was observed in the suprabasilar keratinocytes, which is indistinguishable from the pattern seen in PV or PF. Therefore, an interpretation of IgG4 staining by IHC in cutaneous acantholytic disorders should be approached with caution. Confirmation with DIF would be important in these settings.