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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. There are five variants and the disseminated superficial actinic porokeratosis is relatively common.

Mibelli 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 complete 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 X-linked dominant inheritance.

Porokeratosis Punctata Palmaris et Plantaris (PPPP; 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 punctate 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.

The prefix “poro” comes from the Greek for “callus.”

Isolated cases. The DSAP form is relatively common, whereas the others are rare. The DSAP affects women 3 times more often than men.

Autosomal dominant inheritance, probably with some reduction in penetrance in females. Sporadic occurrence may occur in which a later onset is usual.

Histogenesis thought to be a clonal expansion of abnormal epidermal cells, which in susceptible individuals may be triggered by sunlight, irradiation, trauma, infection, or immunosuppression. Recent evidence showed a chromosomal abnormality with preferential involvement of chromosome 3, region 3p14-p12 being involved. In turn, the chromosomal instability may predispose to malignancy. The development of porokeratosis in immunosuppressed patients may be caused by allogenic inhibition of normal epidermal cells by immunosuppression, allowing phenotypic expression of porokeratosis in genetically predisposed individuals.

Distinctive “crater-like” plaques characterized by narrow horny ridges with central atrophy. The histopathological hallmark is a circumferential cornoid lamella, a parakeratotic horn arising from a cell in the epidermis.

Skin eruption usually begins in childhood ...

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