Mucinous Metaplasia of the Vulva in Zoon Vulvitis and Lichen Sclerosus et Atrophicus. Description of 3 Additional Cases of a Rarely Reported Histopathologic Finding.

Mucinous metaplasia of the vulva (MMV) is a histopathologic finding that has been reported previously in only 3 patients and needs to be distinguished from vulvar extramammary Paget disease. We report 3 additional instances of MMV associated to Zoon vulvitis and vulvar lichen sclerosus et atrophicus. Histochemical and immunohistochemical studies were performed on biopsies from erythematous and erosive vulvar lesions of 3 women aged 64, 80 and 84 years, with features of Zoon vulvitis (2 cases) and lichen sclerosus et atrophicus (1 case). Mucin-containing epithelial cells were present on the uppermost layers of the squamous epithelium. On immunohistochemical study the metaplastic cells were positive for cytokeratin 7, epithelial membrane antigen and carcinoembryonic antigen, thus mimicking the phenotype of Paget disease. MMV is most likely related to chronic inflammation. Cytological and architectural features allow for distinction from Paget disease because the mucin-containing cells of mucinous metaplasia of the vulva lack atypia and are predominantly located on the most superficial layers of the surface epithelium.