Porokeratosis

Porokeratosis is a group of diseases characterized by impaired keratinization.

Porokeratosis is a disease inherited in an autosomal dominant manner. Several clinical variants of porokeratosis have been described, differing in the grouping, quantity and localization of the eruptive elements: porokeratosis of Mibelli, characterized by single elements located mainly on the extremities; superficial disseminated eruptive porokeratosis of Resshigi, distinguished by multiple lesions developing in childhood; linear, neviform (or zosteriform) porokeratosis, usually occurring on the extremities and resembling a linear warty nevus; disseminated superficial actinic porokeratosis, which appears more often in adults after sun exposure and is localized on exposed areas of the body; punctate porokeratosis, characterized by diffuse rashes on the fingers, palms and soles; palmoplantar and disseminated porokeratosis in the form of multiple rashes initially on the palms and soles, then on the trunk and extremities. Three more variants have been described - discrete porokeratosis of the soles with single or multiple conical papules resembling plantar warts, reticular porokeratosis with erythematous rashes in the form of a mesh, localized on the trunk, and disseminated bilateral hyperkeratotic variant of Mibelli's porokeratosis.

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Causes porokeratosis

Porokeratosis is a hereditary disease transmitted in an autosomal dominant manner with reduced penetrance. Immunocompromised states, immunosuppressive diseases, in particular AIDS, and ultraviolet radiation can cause or exacerbate porokeratosis. Dysplasia of varying degrees of severity, the formation of pathological clones of cells that are more sensitive to ultraviolet radiation than the surrounding gifted cells have been identified in the lesions. Instability of chromosome 3 has been detected in cultured fibroblasts, which increases the risk of developing skin neoplasia. There are descriptions of familial cases in the literature.

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Pathogenesis

In the central part of the element, there is a cone-shaped invagination of keratin into the epidermis, sometimes covering its entire thickness. In the center of the invagination, a parakeratotic column (plate) is visible in the horny masses - a characteristic sign of the disease. Under the column, the granular layer is absent, but, in general, this layer is thinned. In the dermis - vascular dilation, perivascular lymphohistocytic infiltrates.

Pathomorphology

All the described clinical variants of porokeratosis are characterized by the same histological picture. The main histological sign is the formation of a corneal plate in a depression of the epidermis filled with corneal masses, which is a column of parakeratotic cells. The depression can be located at the mouth of a sweat gland, at the mouth of a hair follicle, and intrafollicularly. Under the column of parakeratotic cells, the granular layer is absent, and vacuilized dyskeratotic cells are found. In the epidermis, there is hyperkeratosis, and acanthosis and papillomatosis are noted around the corneal plate. Vacuolar degeneration of the cells of the Malpighian layer is possible. In the dermis, under the basal membrane, a nonspecific lymphocytic infiltrate with single plasma cells is found. In superficial actinic porokeratosis, along with the described signs, thinning of the Malpighian layer, vacuolar degeneration of the basal epithelial cells, and a superficial strip-like infiltrate with basophilic degeneration of collagen are observed. N. Inamoto et al. (1984) observed individual necrotic epithelial cells and eosinophilic spongiosis in porokeratosis. Electron microscopic examination revealed that the corneal plate consists of two types of cells. Some of them are similar in shape to spinous cells and contain a pycnotic nucleus, bundles of tonofilaments of varying density, melanosomes, and remnants of organelles, while others are rounded, lack desmosomes, and resemble dyskeratotic cells in their structure. Along the periphery of the horny plate are flat cells containing a substance similar to normal keratin and structures with low electron density resembling organelles. In the cells located under the horny plate, the number of keratohyalin granules and tonofilaments is significantly reduced. Among such cells were rounded cells, in their structure resembling "round bodies" in Darier's disease. Some of the spiny cells under the horny plate were partially or completely destroyed, they contain pycnotic nuclei, vacuoles, hetero- and autophagosomes and tonofilaments aggregated along the periphery of the wall. Intraepidermal destruction of epithelial cells is pathognomonic for porokeratosis and can serve as a diagnostic sign. In some places in the basal layer, intercellular edema and reduplication of the basement membrane are noted. Fibroblasts of the dermis are also in a state of dystrophy, some of them contain phagocytosed collagen fibers. Dystrophy of collagen fibers is observed.

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Histogenesis

According to some authors, the formation of the horny plate occurs as a result of two processes: intraepidermal cell destruction (apoptosis) and keratinization disorders such as dyskeratosis. T. Wade and A.B. Ackerman (1980) attribute the primary importance of inflammatory changes in the dermis in the formation of the horny plate, S. Margheseu et al. (1987) attributed them to microcirculatory disorders, and R. Heed and P. Leone (1970) suggested that the histogenesis of porokeratosis is based on the appearance of a clone of altered epithelial cells at the base of the parakeratotic column that forms the horny plate. The process of destruction of spinous cells is compensated by some increase in the mitotic activity of basal epithelial cells. An imbalance between mitotic activity and apoptosis is the cause of malignancy in porokeratosis foci, as is the appearance of mutant epithelial cells. Pathological DNA ploidy and a neoplastic clone in epidermal cells were detected. It was suggested that porokeratosis is not only an epidermal anomaly. It is possible that its development is caused by pathology of two germ layers.

Symptoms porokeratosis

There are several clinical varieties of porokeratosis.

Clinically, all variants of porokeratosis are characterized by the same morphological element - ring-shaped plaques of various sizes with a sunken atrophic center and a raised hyperkeratotic narrow edge with a groove on the surface. The development of such an element begins with the formation of a keratotic papule, gradually increasing in size, forming a ring-shaped plaque, after regression of which an area of skin atrophy remains. Elements localized on the palms and soles differ somewhat in appearance. Thus, with punctate porokeratosis, they are small depressions 1-3 mm in diameter filled with keratin, with discrete plantar porokeratosis - conical papules resembling plantar warts. Sometimes there are atypical rashes - hyperkeratotic, warty, ulcerating, exudative and giant. The possibility of combining different clinical variants of porokeratosis in the same patient confirms the commonality of their pathogenesis.

Combinations of porokeratosis and psoriasis have been described. Cases of malignant tumors such as squamous cell carcinoma, basalioma, and Bowen's disease in patients with porokeratosis are not uncommon, which allows some authors to consider it a precancerous disease. In this case, malignant growth usually begins in the area of the atrophic center of the ring-shaped plaques.

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Classic porokeratosis of Mibeli

The disease is more common in children, but can develop at any age. The initial element is a horny papule, which, due to eccentric growth, increases in size and turns into a ring-shaped plaque. The rash is usually few in number, plaques of various sizes - from several millimeters to several centimeters, rounded in shape. The central part of the element looks sunken, dry, slightly atrophic, sometimes de- or hyperpigmented, warty or with hyperkeratosis. In the peripheral zone of the lesion, a raised keratotic ridge (border) is clearly visible. Upon careful examination with a magnifying glass, a characteristic sign can be seen on the surface of the border - parallel and paired rows of hyperkeratosis.

The lesions are most often located on the body, arms, legs. The genitals, oral mucosa and cornea may be affected.

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Disseminated superficial actinic porokeratosis

It is most common in the third or fourth decade of life on sun-exposed skin areas. The lesions are usually multiple and clinically resemble classic Mibeli porokeratosis. However, in actinic porokeratosis, parallel, paired rows of hyperkeratosis are often not found on the surface of the border.

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Palmoplantar and disseminated porokeratosis

A rare form of porokeratosis and is more common in adults. The disease begins with the appearance of numerous small, slightly raised papules or plaques on the palms and soles. The lesions then spread to other areas of the body. With this type of porokeratosis, the predisposition of lesions to be localized on areas of the body exposed to sunlight is not noted. However, in 25% of patients, an exacerbation of the disease is observed in the summer.

Linear porokeratosis

Usually begins in childhood. Multiple round papules appear, located unilaterally, linearly, segmentally or zosteriformly on the trunk or limbs, often along the Blaschko line. In clinical presentation, linear porokeratosis is very similar to epidermal nevus. Erosive and ulcerative variants of linear porokeratosis on the face have been described.

Course of porokeratosis

The disease has been present for many years, but cases of spontaneous resolution have been described. In all variants of the clinical course, the skin process can transform into a neoplastic one.

Differential diagnosis

Differential diagnosis includes psoriasis, lichen planus, warts, basal cell carcinoma, granuloma annulare, discoid lupus erythematosus, seborrheic and horny eczema, and epidermal nevi.

Treatment porokeratosis

Keratolytic agents, cryodestruction, intralesional administration of corticosteroids, 5% 5-fluoracil ointment are prescribed; in the actinic form - sunscreen creams; in widespread forms, aromatic retinoids or high doses of vitamin A are recommended.