Extramammary Paget's disease presenting as alopecia neoplastica

Extramammary Paget's disease (EMPD) is a rare malignant neoplasm with a predilection for the apocrine-rich anogenital skin and less commonly for the axilla. The tumor rarely occurs in non-apocrine bearing regions where it is referred to as ectopic EMPD. Here, we report a case of a patient that presented with a poorly circumscribed, erythematous plaque with patchy alopecia on the scalp. Histology showed pagetoid infiltration of the epidermis by atypical single and nested cells with abundant amphophilic cytoplasm with nuclear hyperchromasia, extending along the adnexae. Immunohistochemistry showed that the tumor cells stained positively for mucicarmine, periodic acid schiff, cytokeratin-7, polyclonal carcinoembryonic antigen, epithelial membrane antigen, gross cystic disease fluid protein, androgen receptor and Her-2-neu; and negatively for S-100, HMB-45, CDX-2, thyroid transcription factor-1, estrogen receptor and progesterone receptor, thus, establishing the diagnosis of ectopic EMPD. Subsequent workup showed no underlying malignancy. To our knowledge, we report the second case, and the first in the English literature, of an ectopic EMPD involving the scalp without any associated malignancy.