Widespread Bilateral Systematized Blaschko Linear Porokeratotic Eccrine and Hair Follicle Nevus; A Report of Rare Case

Abstract Porokeratotic eccrine and hair follicle nevus (PEHFN) is an extremely rare, non-hereditary disorder of keratinization characterized by eccrine and hair follicle involvement. To date, only 11 cases have been reported in literature. We present a rare case of systematized Blaschko-linear PEHFN presenting as widespread hyperkeratotic verrucous filiform papules since birth, affecting the face, scalp, trunk, and limbs. Histopathological examination revealed characteristic features of PEHFN, including basket-weave hyperkeratosis, coronoid lamella, and parakeratotic columns. The granular layer was absent beneath the parakeratotic column. Notably, PEHFN has been associated with keratitis ichthyosis and deafness (KID) syndrome, a rare genetic disorder. Our case highlights the importance of recognizing PEHFN’s distinctive clinical and histopathological features and its potential association with KID syndrome, emphasizing genetic counselling for affected individuals. This report contributes to the limited literature on PEHFN, underscoring its classification under the unified term porokeratotic adnexal ostial nevus (PAON).