Primary vulvar extramammary Paget disease associated with herpes simplex virus infection: a rare case report.

Extramammary Paget disease (EMPD) is an uncommon neoplasm with a predilection for apocrine gland-rich areas, such as the anogenital region. Herpes simplex virus (HSV) commonly causes infection in this location. However, the coexistence of both entities within the same lesion is exceptionally rare. We report the case of an 89-year-old woman presenting with a pruritic erythematous vulvar plaque. Skin biopsy revealed intraepidermal glandular proliferation consistent with EMPD, composed of pagetoid cells positive for CK7 and diastase-resistant periodic acid-Schiff (PAS). In addition, acantholytic areas containing multinucleated giant cells with ground-glass nuclei and positive immunohistochemical staining for HSV were identified. Subsequent investigations showed no evidence of an underlying visceral malignancy. The concomitant occurrence of EMPD and HSV is extremely rare, with this representing the fourth reported case in the literature. This case highlights the importance of recognising superimposed HSV infection in EMPD, as it may alter the histological features and pose a diagnostic challenge.