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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.
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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.
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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.
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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.
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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.
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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.
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The prefix “poro” comes from the Greek for “callus.”
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Isolated cases. The DSAP form is relatively common, whereas the
others are rare. The DSAP affects women 3 times more often than men.
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Autosomal dominant inheritance, probably with
some reduction in penetrance in females. Sporadic occurrence may occur in
which a later onset is usual.
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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.
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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.
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Skin eruption usually begins in childhood ...