Widespread Porokeratotic Eccrine Ostial and Dermal Duct Nevus Along Blaschko Lines

: Porokeratotic eccrine ostial and dermal duct nevus is a congenital hamartoma of possible eccrine origin with no malignant potential. It is usually localized at the extremity of a single limb, while wider systematized distribution has rarely been documented. A child with an unusually widespread nevus following Blaschko lines is reported. The disorder had a striking presentation in the form of a systematized linear epidermal nevus composed of multiple tiny filiform keratotic spines, which histologically corresponded to columns of porokeratosis. Serial histopathologic sections of a 4‐mm punch biopsy specimen barely demonstrated an anatomic relationship between the porokeratotic columns and the underlying acrosyringeal duct. This report provides further evidence of porokeratotic eccrine ostial and dermal duct nevus being distributed along Blaschko lines, thus confirming it is a peculiar epidermal nevus due to a mosaic cutaneous condition.