Giant verrucous porokeratosis of Mibelli mimicking psoriasis in a patient with psoriasis.

Porokeratosis of Mibelli is a disorder of epidermal keratinization characterized by annular plaques with an atrophic center surrounded by a keratotic wall. We report a case of a giant verrucous porokeratosis of Mibelli mimicking psoriasis that developed in a patient with psoriasis and therefore went unrecognized for a long time. Histologically the lesion combined features of porokeratosis at the periphery and of psoriasis at its center, a picture recently described as "psoriasis encircled by porokeratosis." The possible pathogenetic relationship between psoriasis and the development of porokeratosis is also discussed.