Pseudoepitheliomatous hyperplasia in lichen sclerosus of the vulva.

Small tentacles or separated nests of squamous cells in the dermis are not uncommonly seen in long-standing vulvar lichen sclerosus (LS) associated with epidermal thickening. We recently encountered a case where separated nests of well-differentiated squamous cells in the dermis were difficult to distinguish from squamous cell carcinoma (SCC). Further biopsies showed similar nests originating from every hair follicle. We postulated a diagnosis of multifocal pseudoepitheliomatous hyperplasia (PEH) to explain this phenomenon. Because we could find no reference to PEH in the setting of LS, we reviewed the biopsies of 92 women with extragenital and vulvar LS with and without carcinoma to determine its frequency and histological appearance. The study population, which excluded the index case, comprised 10 women with extra-anogenital LS, 58 with vulvar LS without carcinoma, and 24 with vulvar LS with carcinoma. The presence of PEH, epidermal thickness, predominant dermal collagen change, degree of inflammation, and presence of fibrin and red blood cells were recorded. The presence or absence of lichen simplex chronicus (LSC), squamous cell hyperplasia (SCH), and differentiated vulvar intraepithelial neoplasia (VIN) were recorded. PEH was identified only in vulvar LS, where it was seen in 7/58 (12.1%) women without carcinoma, 1/24 (8.3%) with carcinoma, and 0/10 (0%) with extra-anogenital LS. Two forms of PEH were seen: predominantly epidermal 7/8 (87.5%) and predominantly follicular 1/8 (12.5%). PEH was associated with increased epidermal thickness, less dermal edema, more dermal inflammation, fresh fibrin, and red blood cell extravasation. In all cases, there was associated LSC, but there was no SCH or differentiated VIN. In conclusion, PEH may explain many of the cases of dermal tentacles and separated squamous nests in vulvar LS with LSC. The association with fresh fibrin and red blood cells suggests that PEH might be a reaction to tissue damage. PEH is distinguished from SCC by its lack of atypia, confinement to the abnormal collagen, and limited growth. The pathologist must be careful about making a diagnosis of PEH in LS with epidermal thickening, looking carefully for basal atypia and other features of differentiated VIN in the overlying epidermis or dermal proliferation. We do not know whether PEH occurs in differentiated VIN and, if it does, how it could be distinguished from SCC.