| Summary: | Introduction: In patients with autoimmune skin blistering diseases (ABDs), the diagnostic gold standard has classically been direct and indirect immunofluorescence (DIF and IIF), despite inherent technical problems of autofluorescence. Aim: We sought to overcome autofluorescence issues and compare the reliability of immunofluorescence versus immunohistochemistry (IHC) staining in the diagnoses of these diseases. Methods: We tested via IHC for anti-human IgG, IgM, IgA, IgD, IgE, Kappa light chains, Lambda light chains, Complement/C3c, Complement/C1q, Complement/C3d, albumin and fibrinogen in 30 patients affected by a new variant of endemic pemphigus foliaceus in El Bagre, Colombia (El Bagre-EPF), and 30 control biopsies from the endemic area. We also tested archival biopsies from patients with ABDs whose diagnoses were made clinically, histopathologically and by DIF/IIF studies from 2 independent dermatopathology laboratories in the USA. Specifically, we tested 34 patients with bullous pemphigoid (BP), 18 with pemphigus vulgaris (PV), 8 with pemphigus foliaceus (PF), 14 with dermatitis herpetiformis (DH) and 30 control skin samples from plastic esthetic surgery reduction surgeries. Results: The diagnostic correlation between IHC and DIF-IIF was almost 98% in most cases. IHC revealed evidence of autofluorescence around dermal blood vessels, dermal eccrine glands and neurovascular packages feeding skin appendices in ABDs; this autofluorescence may represent a non-specific immune response. Strong patterns of positivity were seen also in endothelial-mesenchymal cell junction-like structures, as well as between dermal fibrohistiocytic cells. In PV, we noted strong reactivity to neurovascular packages supplying sebaceous glands, as well as apocrine glands with edematous changes. Conclusions: We suggest that IHC is as reliable as DIF or IIF for the diagnosis of ABDs; our findings further suggest that what has previously been considered DIF/IIF autofluorescence background may be of relevance in ABDs. Our discovery of reactivity against edematous dermal apocrine glands may be related to the fact that PV has a vegetant form, with lesions present in anatomic areas where these glands exist.
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