Histopathological and immunohistochemical studies of poroid hidradenoma.

Poroid hidradenoma (PH), a less common subtype of poroid neoplasm (PN) than eccrine poroma (EP), has not been immunohistochemically studied before. Six cases of PH (four solitary PH and two PH coexisted with other types of PN) were included in the study. Fifteen cases of EP were also included for comparison. Hematoxylin and eosin, Masson-Zimmerman silver stain, and a variety of immunohistochemical stains were used. Microscopically, PH is not connected to the epidermis. All six PH contained small poroid cells and larger, paler cuticular cells. Some PH showed separate or clusters of sebocytes (2/6), horn cysts (1/6), juxtaposed lymphoid follicles in the stroma (1/6) and foci of keratohyaline granules (2/6), none of which was seen in the 15 EP. Immunohistochemically, the keratin distribution of PH was very similar to that of EP. PH has a very small number of Langerhans cells (significantly lower than the overlying epidermis, P=0.045), and a sparse deposition of melanin. We conclude that except the location, the histopathological and immunochemical differences between PH and EP were small. Sebaceous differentiation in two PH lesions suggested the possibility of an apocrine origin. The deeper parts of eccrine apparatus other than basaloid cells may have been more actively involved in the histogenesis of PH.