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Pigmentary Disorders: Introduction

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  • Normal skin color is composed of a mixture of four biochromes, namely, (1) reduced hemoglobin (blue), (2) oxyhemoglobin (red), (3) carotenoids (yellow; exogenous from diet), and (4) melanin (brown).

  • The principal determinant of the skin color is melanin pigment, and variations in the amount and distribution of melanin in the skin are the basis of the three principal human skin colors: black, brown, and white.

  • These three basic skin colors are genetically determined and are called constitutive melanin pigmentation; the normal basic skin color pigmentation can be increased deliberately by exposure to ultraviolet radiation (UVR) or pituitary hormones, and this is called inducible melanin pigmentation.

  • The combination of the constitutive and inducible melanin pigmentation determines what is called the skin phototype (SPT) (see Table 10-2). Ethnicity is not necessarily a part of the definition, e.g., African “black” ethnic persons can be SPT III and an East Indian Caucasian can be SPT IV or even V. The SPT is a marker for skin cancer risk and should be recorded at the first patient visit (Fig. 13-1).

  • Increase of melanin in the epidermis results in a state known as hypermelanosis. This reflects one of two types of changes:

    • An increase in the number of melanocytes in the epidermis producing increased levels of melanin, which is called melanocytic hypermelanosis (an example is lentigo).

    • No increase of melanocytes but an increase in the production of melanin only, which is called melanotic hypermelanosis (an example is melasma).

  • Hypermelanosis of both types can result from three factors: genetic, hormonal (as in Addison disease), and UVR (as in tanning).

  • Hypomelanosis is a decrease of melanin in the epidermis. This reflects mainly two types of changes:

    • A decrease of the production of melanin only that is called melanopenic hypomelanosis (an example is albinism).

    • A decrease in the number or absence of melanocytes in the epidermis producing no or decreased levels of melanin. This is called melanocytopenic hypomelanosis (an example is vitiligo).

  • Hypomelanosis also results from genetic (as in albinism), from autoimmune (as in vitiligo), or other inflammatory processes (as in postinflammatory leukoderma in psoriasis).

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Figure 13-1.

This image demonstrates the protective role of melanin. It shows the hypomelanotic lower arm of a patient with piebaldism (a very rare genetic syndrome which is caused by mutations of the KIT protooncogene and results in a developmental patchy loss of melanocytes and thus in depigmented patches of skin) that exhibits dermatoheliosis including multiple solar (actinic) keratoses, whereas the normally pigmented upper arm is devoid of these lesions.

Graphic Jump Location
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Vitiligo

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ICD-9: 709.01 ○ ICD-10: L80 Image not available.

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  • Worldwide occurrence; 1% of population affected.

  • A major psychological problem for brown or black persons, resulting in severe difficulties in social adjustment.

  • A chronic disorder with multifactional predisposition and triggering factors.

  • Clinically characterized by totally ...

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