Congenital or acquired genodermatosis disorder of keratinization. Clinically, presents one or more atrophic patches surrounded by a distinctive ridge-like border called the cornoid lamella. Several variants are described with the disseminated superficial actinic porokeratosis being relatively common.
Mibelli Porokeratosis; Porokeratosis Actinic Disseminated Superficial; Porokeratosis Plantaris et Disseminata; Porokeratosis Punctata Palmaris et Plantaris; Porokeratosis Linearis.
Named after the description of Italian dermatologist Vittorio Mibelli in 1889. The prefix “poro” comes from the Greek for “callus.”
Variants of Porokeratosis
Porokeratosis of Mibelli: It is a rare keratoatrophoderma characterized by cutaneous centrifugally spreading patches. The lesions are surrounded by narrow horny ridges and with central atrophy and appear as crater-like formations.
Porokeratosis Actinic Disseminated Superficial Type I (DSAP I): It is characterized by the existence of photosensitivity developing after the age of 16 years and completes clinical manifestation during the fourth decade. It is much more frequent than the porokeratosis of Mibelli from which it must be distinguished.
Porokeratosis Actinic Disseminated Superficial Type II (DSAP II): Similar to the DSAP1 in clinical presentation. However, a hereditary condition only reported in a Chinese family.
Porokeratosis Plantaris et Disseminata: A type of porokeratosis most probably distinct from both the Mibelli and disseminated superficial actinic types. The clinical features include lesions that appear first on the palms and soles during the late teens and early twenties. It is a chronic progressive disorder of keratinization with annular or gyrate plaques showing elevated borders. It is consistent with either an autosomal or an X-linked dominant inheritance.
Porokeratosis Linearis: Rare congenital variant may develop in adults. Lesions are grouped and linearly arranged along Blaschko lines, reminiscent of an epidermal nevus, linear psoriasis, or lichen striatus. It exists in two forms: Localized form, where lesions are unilateral and confined to one commonly distal extremity. In the generalized form, lesions are multiple, affect several extremities, involve the trunk, and may appear in a zosteriform pattern.
Porokeratosis Punctata Palmaris et Plantaris (PPPD Syndrome; Keratoderma Palmoplantar Punctate Type II): A disease characterized by spinous keratoses on the volar aspects of the hands and feet that appear in the early twenties. The nails, teeth, and sweating system are normal. Histologically, studies show columnar parakeratosis that resembled the cornoid lamella of porokeratosis. This condition can be classified as Type II punctuate palmoplantar keratoderma (PPK), Type I being the Buschke-Fischer-Brauer disorder, and Type III being acrokeratoelastoidosis. It is considered a hereditary disorder transmitted as an autosomal dominant pattern.
Other Rarer Variants: Porokeratosis ptychotropica, facial porokeratosis, giant porokeratosis, hypertrophic verrucous porokeratosis, reticulate porokeratosis, and eruptive pruritic papular porokeratosis.
Isolated cases. The DSAP form is relatively common, whereas the others are rare. The DSAP affects women three times more often than men. Porokeratosis occurs rarely in dark-skinned people. Caucasians (Italians) are at higher risk.