Porokeratosis mibelliQ82.8

Rare, to the porokeratoses (naming: poros = opening; keras = horn; incorrect name, because the keratinization anomaly originates neither from the follicular epithelium nor from the acrosyringium), irregular autosomal-dominant inherited, but also spontaneously occurring, usually sharply bordered to the healthy skin, differentiation disorder of the epidermis with firm keratotic papules which are configured to areal, sometimes map-like or also garland-shaped. The hallmark is a histological phenomenon a so-called "corneal lamella", a slough-shaped parakeratosis (corneal lamella) in the midst of a hyperkeratosis.

Scappaticci et al (1989) found clonal chromosomal abnormalities with preferential involvement of chromosome 3 in three siblings and one sporadic case with this disorder. The 3p14-p12 region, which comprises the most common fragile site in humans, was particularly affected. Scappaticci et al (1989) concluded that Mibelli's porokeratosis is associated with chromosomal instability and that this in turn may predispose to malignancy.

From a cohort of 134 Chinese subjects with porokeratosis who were examined for mutations in isoprenoid genes, Zhang et al. (2015) identified 6 different heterozygous mutations in the PMVK gene in 9 affected individuals. The mutations were not found in 270 ethnically matched controls. Although all 9 patients had Mibelli-type porokeratotic lesions, they also had other subtypes of porokeratosis:

5 had a porokeratoma,

4 had genital porokeratosis,

3 had hyperkeratotic porokeratosis

1 had linear porokeratosis.

This overview proves that a different phenotype can be expressed with the same gene type. None of the affected individuals had >100 lesions (4 of them had 10 or less). The size of the lesions ranged from 0.5 cm to 5.0 cm in diameter. Zhang et al. (2015) observed that even within a family, affected individuals carrying the same mutation had different clinical manifestations and different degrees of severity. All lesions examined showed the histological phenomenon of the "cornoid lamella".

Mainly occurring during childhood and adolescence, but also in later adulthood.

Men are affected twice (3 times) as often as women.

Apparently, however, there are families with more than 1 variant of a porokeratosis type, so that different phenotypes are apparently expressed with a common genotype. In this respect, a specific phenotype cannot always be assigned to a specific genotype.

If the hands are affected, the nails close to the heart may be affected (nail dystrophy with longitudinal ridging of the nail plate).

Extremities (especially forearms, lower legs and back of hands) are affected, rarely also trunk, face, glans penis or vulva. Mucosal involvement and rarely involvement of the cornea are possible.

Usually single or few (rarely multiple: differentiation from disseminated type difficult!), slowly growing, brownish keratotic papule. The initial focus is often mistaken for a blackhead. The onset of the disease often falls in childhood.

Initial: 0.1-0.2 cm in size, usually solitary, yellowish, yellowish or reddish brown, asymptomatic papules with adherent, non-detachable, central horny spine. The horny papules may become painful if there is continuous lateral pressure (e.g., from footwear). Due to gradual growth in area and thickness (random) confluence of the individual papules. This results in roundish, circular or garland-shaped plaques up to 0.5-10.0 cm in size (or even larger) sharply separated from the healthy skin with a verrucous or even slightly atrophic surface, porokeratosis mibelli gigantea, see illustrations. Centrifugal growth may persist until middle age and then stop. Associated symptoms: nail deformities.

Vent-like parakeratosis, cornoid lamella, atypical basal cells, focal lymhohistiocytic infiltrate in the upper corium.

Keratosis actinica: only on UV-exposed areas; painful, red, keratotic plaques

Lupus erythematosus chronicus discoides: UV-exposed sites, painfulness, histology and immunohistology are diagnostic

Granuloma anulare: surface smooth nodules and plaques, asymptomatic,

Keratosis follicularis: follicle-related red keratoses, extensor localization

Lichen planus anularis: smooth red oerated surface, miest combined with mucosal involvement

Psoriasis vulgaris: extensor, filled scaly plaques, no anular structures

Tinea corporis: mycological-culteral evidence

Tuberculosis cutis verrucosa:diascopic evidence of brownish infiltrates, wrinkled atrophy of the skin

Elastosis perforans serpiginosa: initially 0.2-0.5 cm in size, red, firm, smooth or slightly keratotic, asymptomatic (mild itching possible) papules aggregating into anular or serpiginous plaques with hyperkeratotic overgrowth. Subsequently, the clinical picture is characterized by peripheral progression and central healing tendency, so that anular formations (up to 5.0-7.0 cm in diameter) are even more accentuated.

Biannual skin checks to exclude lesional carcinoma formation.

Ablation with the help of cryosurgery (open spray method), electrocoagulation,_CO2- or Erbium-YAG- laser. Therapeutic successes are not satisfactory.

In multiple flocks, porokeratosis superficialis disseminata actinica should be considered in the first instance.

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4. Mibelli V (1893) Contributo alla studio della ipercheratosi dei canali sudoriferi (porokeratosi). G Ital Dermatol Venereol (Torino) 28: 313-355.
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