Forms of epithelial differentiation of draining sinus in acne inversa (hidradenitis suppurativa)

The draining sinus is a late complication of several forms of severe acne, leading to extensive, periodically inflamed lesions that are undermined by a system of fistulas, supposed to be of follicular origin. We investigated the expression of various cytokeratins (CKs) and desmosomal proteins in the draining sinus of acne inversa (hidradenitis suppurativa) using monoclonal antibodies in immunohistochemistry on paraffin-embedded sections. We were able to define three different phenotypes of stratified squamous epithelia covering the sinus tracts. Type I epithelium was cornifying and characteriz ed by the presence of CK 10, desmogleins 1-3 and desmocollins 1-3 in an epi dermis-like pattern. Type II epithelium was non-cornifying, negative for CK 10 and positive for CK 13, It was negative for desmocollin 1 but strongly immunopositive for desmoglein 1 suprabasally and for desmoglein 2 in the ba sal cells. Type LII epithelium was non-cornifying and strongly inflamed. It was marked by the presence of CK 7, CK 19 and desmoglein 2 and the absence of CK 10, desmoglein 1 and desmocollin 1. In both type II and III epitheli um, desmoglein 3, desmocollin 2 and desmocollin 3 showed an inverted staini ng pattern as compared with normal epidermis and type I epithelium. Desmogl ein 2 and CIC 5/14 always remained restricted to the basal cell layer. Anti bodies against CK 6 and CK 13/15/16 were immunopositive in all three phenot ypes and CK 17 was predominantly immunolocalized to suprabasal layers of ty pe II and III epithelium. The three phenotypes are characterized as patholo gical stratified squamous epithelia reflecting the dynamic process of infla mmation, proliferation and stratification taking place in acne inversa.