Follicular porokeratosis: distinct clinical entity or histologic variant?

Various clinical subtypes of porokeratosis, clinically characterized by annular plaques with a normal or atrophic center and a distinctive keratotic ridge, are described based on the age of onset, size, number and distribution of the lesions. Follicular involvement, identified by follicular localization of cornoid lamellae, is uncommon and has only been reported in association with other subtypes such as disseminated superficial actinic porokeratosis and porokeratosis of Mibelli. We present a case of follicular porokeratosis in a 40-year-old male who presented initially with scaly red "papules" in a follicular distribution on the upper extremity. Microscopic examination of a punch biopsy specimen revealed parakeratosis confined to the follicle and mild interface change. A repeat biopsy performed in 2008 revealed identical histologic features. In terms of etiopathogenesis, a clone of cells at the base of the follicle demonstrating abnormal keratinization is not a novel concept and has been demonstrated in other porokeratotic dermatoses. However, the presence of lesions that are solely follicular based, in terms of clinical presentation and histologic findings, and static over a 3-year period favors the concept that follicular porokeratosis is a distinct clinical entity and not merely a histologic variant of the porokeratotic dermatoses described in the literature thus far.