Melanoma Masquerading as a Zosteriform Rash

Zosteriform Lymphangitic Metastases of Eccrine Porocarcinoma

Eccrine porocarcinoma (EPC) is a rare malignant neoplasm which originates from the intraepidermal portion of eccrine sweat glands or acrosyringium. Here, we report a unique case of cutaneous metastases of EPC presenting with an erosive plaque on the left thumb and multiple nodules on left forearm. The histopathological examination of the wrist lesion revealed islands of basaloid tumor cells with eosinophilic cytoplasm, downward infiltrating growths, ductal differentiation, and intracytoplasmic lumen formations and focally connected to the epidermis. Acrosyringeal differentiation was confirmed by positive immunohistochemical staining using antibodies to carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) in some of porocarcinoma cells. Lymphatic embolization was shown by immunostaining of podoplanin. To the best of our knowledge, this is the first reported EPC case with a primary lesion on the left thumb and zosteriform growth pattern of lymphangitic metastases on left forearm. Our case highlights the diagnostic challenges and reveals lymphangitic metastasis mode of EPC.