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SECTION 12: DISORDERS OF PIGMENTATION

INTRODUCTION

Skin color is genetically determined and is caused by the total amount of melanin pigment in the skin. Normal constitutive melanin pigmentation determines skin type, which is classified by the Fitzpatrick skin phototypes as follows:

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Skin Phototypes Ability to Tan Susceptibility to Burns

SPT I

Never tans, white skin

Sunburns easily

SPT II

Tans with difficulty

Sunburns easily

SPT III

Can tan with time

Occasionally burns

SPT IV

Tans easily

Rarely burns

SPT V

Tans easily, brown skin

Rarely burns

SPT VI

Tans easily, black skin

Rarely burns

Disorders of hypopigmentation are caused by decreased melanin content in the skin owing to decreased or absent melanin production or melanocytes (specialized cells of the epidermis that produce and store melanin). Disorders of hyperpigmentation are caused by increased melanin content in the skin owing to an increase in melanin production or melanocytes.

DISORDERS OF HYPOPIGMENTATION

Decreased or absent melanin in the skin can lead to hypomelanosis and can occur by two main mechanisms.

  1. Melanocytopenic hypomelanosis: absent or decreased number of melanocytes (e.g., vitiligo).

  2. Melanopenic hypomelanosis: absent or decreased melanin production, but normal number of melanocytes [e.g., oculocutaneous albinism (OCA)].

PITYRIASIS ALBA

Pityriasis alba is a common asymptomatic, sometimes scaly, hypopigmentation of the face, neck, and body.

INSIGHT image

Pityriasis alba entails both mild dermatitis and pigment alteration; generally, the former responds quickly while the latter continues to be an issue for many months or years.

EPIDEMIOLOGY

AGE Young children, often between the ages of 3 and 16 years.

GENDER M = F.

RACE All races, more noticeable in darker skin types.

PREVALENCE Common.

ETIOLOGY Likely a form of atopic dermatitis.

PATHOPHYSIOLOGY

Pityriasis alba is thought to be an eczematous dermatosis, with hypomelanosis resulting from postinflammatory changes and ultraviolet screening effects of the hyperkeratotic (increased thickness) and parakeratotic (inappropriately maturing) epidermis.

HISTORY

Hypopigmented areas are usually stable then gradually disappear with age. Some lesions may persist into adulthood. The areas are typically asymptomatic, but can sometimes burn or itch.

PHYSICAL EXAMINATION

Skin Findings

TYPE Macules, may have slight scale.

NUMBER One to twenty lesions may be present.

COLOR Pink, then off-white to tan-white. Can repigment over time.

SIZE AND SHAPE 5 to 30 mm or larger.

DISTRIBUTION Face (malar region), neck, trunk, extremities.

SITES OF PREDILECTION Face, especially the cheeks (Fig. 12-1), midforehead, and around the eyes and mouth.

FIGURE 12-1
Pityriasis alba
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