Epidermal nevus is a benign developmental defect, which, as a rule, has a dysembryogenetic origin. Three forms of a nevus are known: localized, inflammatory, systemic. All of them appear at birth or in early childhood.
Localized nevus is clinically a limited lesion consisting of exophytic single or multiple papillomatous formations closely adjacent to each other, rounded, oval or irregular in shape, color of normal skin or with varying degrees of pigmentation, with a smooth or (more often) erectile surface.
Inflammatory nevus usually has the form of compacted, linearly grouped elements with a verruxic surface on the inflamed base, often psoriasis, sometimes accompanied by itching.
In systemic nevus, foci are arranged linearly, in the form of garlands, mostly monolaterally, sometimes in combination with defects in the development of eyeballs, skeletal anomalies (especially the bones of the skull) and encephalopathies.
Pathomorphology. Typical elements are warty hyperkeratosis, acanthosis, papillomatosis. With inflammatory form in the papillary layer of the dermis, there is a nonspecific mononuclear infiltrate, in the epidermis - focal parakeratosis. With localized and systemic forms of the nevus, pilosebate structures often occur, which undergo hypertrophy in the pubertal period. When localized on the scalp, the defects can be of complex structure and contain clusters of hypertrophied apocrine glands. In some cases, the systemic nevus is accompanied by acantholytic hyperkeratosis, similar to the bullous variant of congenital ichthyosiform erythroderma. At the same time, a granular degeneration of epithelial cells with a rupture of cellular contacts, perinuclear swelling and an increase in the number of keratogialin granules of irregular shape are observed in the prickly layer. In the foci of inflammatory nevus, morphological changes may resemble those in psoriasis.
Differentiate the epidermal nevus from vulgar warts in patients with immunodeficiency, actinic precancerous hyperkeratosis, acanthosis nigricans, and verruzed psoriasis. In vulgar warts, in addition to the vacuolization of epitheliocytes, intra- and extracellular viral inclusions are observed on the granule of prickly and granular layers, the type of which can be determined by the method of in situ hybridization, parakeratosis and warty dyskeratosis.
With actinic precancerous hyperkeratosis, suprabasal acantholysis, atypical cells and a small inflammatory reaction are observed.
The lesion with acanthosis nigricans is localized in the intertriginoid regions, the histological pattern is characterized by acanthosis and pronounced hyperpigmentation of the basal layer cells.
Differential diagnosis of inflammatory nevus with verruzed form of psoriasis and in some cases is so difficult that sometimes these conditions are identified