Hypopigmentation and depigmentation of the skin: causes, symptoms, diagnosis, treatment

Hypopigmentation and depigmentation of the skin are accompanied by a significant decrease or complete disappearance of melanin. They can be congenital and acquired, limited and diffuse. An example of congenital depigmentation is albinism.

Ocular-cutaneous albinism is a heterogeneous disease characterized by the absence or a sharp decrease in pigment in the skin, hair and iris of the eye. Two forms of ocular-cutaneous albinism - tyrosinase-negative and tyrosinase-positive - are associated with the absence or insufficient activity of tyrosinase. The mechanism of development of other forms (Chediak-Higashi, Hermansky-Pudlak syndromes, etc.) has not yet been clarified.

Pathomorphology. The pigment melanin is not detected. Melanocytes have normal morphology, are evenly distributed (except for the "black curl - albinism - deafness" syndrome), but their pigment-synthesizing function is reduced. In the tyrosinase-negative variant, melanosomes are at stage I, less often - at stage II of maturation, in the tyrosinase-positive variant - at stage III. Giant melanosomes have been described in Hermansky-Pudlak and Chediak-Higashi syndromes. In addition, in Chediak-Higashi syndrome, large cytoplasmic inclusions are found in mast cells of the skin (stained with toluidine blue).

Limited depigmentation includes vitiligo, which is characterized by hypomelanosis of the skin caused by the absence of melanocytes.

Vitiligo. The nature of the dermatosis is unknown, but there is data on the role of immune and metabolic disorders, neuroendocrine disorders, and exposure to ultraviolet rays (sunburn). The presence of familial cases indicates a possible role of a genetic factor. It can also manifest as paraneoplasia, or be a result of exogenous diseases, including occupational diseases. Clinically, it is characterized by the presence of milky-white spots of various sizes and shapes, surrounded by normal skin or a strip of hyperpigmentation. The disappearance of the pigment can be complete or partial, in the form of a mesh or small pinpoint spots. Depigmentation may be preceded by an erythema stage. Very often, the hands are affected first, which is not observed in autosomal dominant congenital vitiligo (piebaldism). Lesions can be localized on the entire skin. Depending on the prevalence of the process, focal, segmental and generalized forms are distinguished.

Pathomorphology. As a rule, no major changes are observed in the lesions. The epidermis is of normal thickness or slightly thinned, its outgrowths are smoothed. The stratum corneum is mostly thickened, the granular layer consists of one row of cells with scanty granularity. The spinous layer is without any significant changes, the cells of the basal layer contain almost no pigment. However, with hypopigmentation, it is sometimes detected, although in small quantities. Melanocytes are almost never found in depigmented skin, and in hypopigmented areas there are fewer of them than normal. In the dermis, swelling and homogenization of individual collagen fibers is observed, the elastic network is without any significant changes. The vessels are usually dilated, their walls are thickened, and nested accumulations of fibroblasts, histiocytes, and tissue basophils are located around them. The epithelial hair follicles in the depigmented areas are somewhat atrophic, their mouths are dilated, filled with horny masses, the sebaceous glands are also atrophic. Electron microscopic examination of the skin at the border of the vitiligo lesion shows an increase in the number of epidermal macrophages and destructive changes in melanocytes, affecting all structures of these cells. In the foci of long-standing vitiligo, melanocytes and melanin-containing structures in the epithelial cells are absent. According to some authors, the number of epidermal macrophages in the vitiligo lesion is increased, their activity is significantly increased. In areas of outwardly healthy skin, melanocytes contain melanosomes and premelanosomes, but not a complex of melanosomes, which are the highest degree of organization of melanin granules. This indicates insufficiency of the melanocyte function.

The histogenesis of vitiligo remains unclear. Some authors associate vitiligo with dysfunction of the autonomic nervous system, others - with decreased production of melanocyte-stimulating hormone. R.S. Babayants and Yu.I. Lonshakov (1978) consider melanocytes in this disease to be defective and incapable of responding to the action of melanocyte-stimulating hormone, Yu.N. Koshevenko (1986) obtained data indicating the presence in depigmented skin of cellular immune reactions involving the C3 component of complement, capable of causing damage to melanocytes.

Acquired depigmentation can be observed in case of occupational hazards (occupational leukoderma), use of medications (drug-induced leukoderma), at the site of inflammatory elements (psoriasis, sarcoidosis, leprosy), syphilis, and pityriasis versicolor (secondary leukoderma).

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