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Pityriasis Alba
Background: Pityriasis alba (PA) is a relatively common skin disorder in children and young adults. It is characterized by the presence of ill-defined, scaly, faintly erythematous patches that subside to leave areas of hypopigmentation. Lesions may progress through the following 3 clinical stages:
  • Papular (scaling) erythematous
  • Papular (scaling) hypochromic
  • Smooth hypochromic

Lesions eventually subside, leaving areas of hypopigmentation that slowly repigment to normal. Duration of PA varies from 1 month to 10 years, but most cases resolve over several months to 1 year. Diagnosis is made clinically and treatment consists of skin care and education of the parents about the benign nature of the disorder. Hydrocortisone may decrease erythema, scale, and pruritus, if present. PA is a nonspecific finding that is commonly associated with atopic dermatitis. Etiology is unknown.

Pathophysiology: In a study of 9 patients with extensive PA, there was reduction in the density of functional melanocytes in the affected areas without any change in cytoplasmic activity. The melanosomes tended to be fewer and smaller, but their distribution pattern in the keratinocytes was normal. Melanosomal transfer to keratinocytes was generally not disturbed. Histology was nonspecific. Hyperkeratosis and parakeratosis were not consistently present, and it seems unlikely that they played a significant role in the pathogenesis of the hypomelanosis. A variable degree of intercellular edema and intracytoplasmic lipid droplets were present. Hypopigmentation may be primarily due to the reduced numbers of active melanocytes and a decrease in number and size of melanosomes in the affected skin.

Frequency:

  • In the US: Although the exact incidence has not been described, up to one-third of school-aged children may have this disorder. PA is not seasonal, but the dry, slightly scaling appearance tends to worsen during cold months, when the air is relatively dry inside the home. In addition, sun exposure may make the lesions more obvious during spring and summer. The condition is more common in patients with a history of atopy.
  • Internationally: In a large study of 9,955 schoolchildren aged 6-16 years who lived in a tropical region the prevalence of PA was 9.9%.

Mortality/Morbidity:

  • PA is generally self limited and asymptomatic.
  • Cosmetic appearance may be an issue in some patients.
  • Day-care facilities and schools may voice concern about the disorder and request the child be evaluated to rule out an infectious disease.

Race:

  • PA occurs in all races.
  • One study found the incidence to be slightly higher in light-skinned races.
  • The condition is frequently more apparent and cosmetically bothersome in patients with darker complexions.

Sex:

  • There is an equal incidence in boys and girls.

Age:

  • PA is most common in children aged 3-16 years. Ninety percent of cases occur in children younger than 12 years.
  • PA occasionally occurs in adults.

History:

  • PA generally is asymptomatic but may be mildly pruritic.
  • Patients may describe any of the following 3 clinical stages:
    • Papular erythematous
    • Papular hypochromic
    • Smooth hypochromic
  • Initially, erythema may be conspicuous and there may be minimal serous crusting of some lesions; however, because the erythema is usually very mild, most parents do not recall the erythematous stage.
  • Recurrent crops of new lesions may develop at intervals.
  • Duration of PA varies from 1 month to 10 years. The average duration of the common facial form in childhood is 1 year or more.
  • Important aspects of patient history
    • Patient or family history of asthma, hay fever, or eczema in the characteristic areas of atopic dermatitis: PA is a nonspecific finding that is commonly associated with atopic dermatitis.
    • The patient may have prior history of rash or eczema at the sites of hypopigmentation; skin irritation produced by any of a variety of causes may heal with postinflammatory hypopigmentation.
    • Ask about prior therapy; potent topical steroids may produce hypopigmentation. Patients may develop irritant or allergic contact dermatitis to a variety of topical creams, lotions, and medications. When these are discontinued and the area recovers from the contact dermatitis, an area of postinflammatory hypopigmentation may occur.
    • Look for seasonal variations in appearance; the scaling areas of hypopigmentation frequently develop during winter, but become more apparent following sun exposure during the spring and summer.

Physical:

  • Characteristic lesions
    • PA is characterized by hypopigmented, round-to-oval, scaling patches on the face, upper arms, neck, or shoulders. The legs and trunk are less commonly involved.
    • Lesions vary in size, usually 1-4 cm in diameter.
    • Most commonly, patients have multiple lesions that range in number from 4 or 5 to 20 or more.
    • Scales are fine and adherent.
  • Affected areas
    • In approximately one-half of all patients, the lesions are limited to the face. In children, the lesions are often confined to the face. The areas around the mouth, chin, and cheeks are the most commonly affected.
    • In 20% of affected children, the neck, arms, and shoulders are involved in addition to the face.
    • Less commonly, the face is spared and there are scattered lesions on the trunk and limbs.
    • Rarely, the disease may be quite extensive. Extensive PA presents with numerous lesions on the trunk and extremities. This form of PA generally occurs in older patients and the lesions may be more persistent.
  • Important aspects of examination
    • Examine for keratotic lesions on the elbows and knees and for small pits in the nails, which may suggest a diagnosis of psoriasis.
    • Examine for the following potential signs of atopic dermatitis:
      • Eczema in the popliteal or antecubital fossa
      • Nipple eczema
      • Cheilitis
      • Dennie-Morgan infraorbital fold
      • Anterior neck folds
      • Wool intolerance
      • White dermographism
      • Infra-auricular fissuring

Causes:

  • No definitive etiologic agent has been described.
  • Excessively dry skin, which is frequently exacerbated by cold, dry environments, appears to be a common factor.
  • Lesions are visible primarily in contrast to dark skin. Increasing sunlight in spring and summer makes them more apparent.
  • The condition is not contagious and no infectious agent has been identified.

Other Problems to be Considered:

Hypopigmented mycosis fungoides
Nevus depigmentosus
Nummular eczema
Pigmenting PA
Psoriasis
Seborrhea
Tinea corporis
Vitiligo

  • Hypopigmentation
    • Any inflammatory process involving the skin, such as contact dermatitis, can leave areas of hypopigmentation upon healing.
    • This may occur in other disorders, including those caused by fungi (eg, tinea versicolor), previous inflammatory conditions (postinflammatory hypopigmentation), or idiopathic disorders (vitiligo). Hypopigmentation may also result as a side effect of medications such as retinoic acid, benzoyl peroxide, and topical steroids.
    • The most common disorders of hypopigmentation in children are PA, vitiligo, nevus depigmentosus, and tinea versicolor.
  • Nevus depigmentosus
    • The localized form of nevus depigmentosus must be distinguished from an ash leaf spot, the earliest cutaneous manifestation of tuberous sclerosis, whereas the systematized form may be confused with hypomelanosis of Ito, another neurocutaneous disorder
  • Nummular eczema
    • Nummular eczema is intensely pruritic.
  • Pigmenting PA
    • This condition seems to be a variant of classic PA, showing a strong association with dermatophyte infection, especially tinea capitis. It may be related to lichenoid melanodermatitis.
    • Characteristic morphology of pigmenting PA includes a central zone of bluish hyperpigmentation surrounded by a hypopigmented, slightly scaly halo of variable width. Patients display lesions primarily on the face.
  • Psoriasis
    • In older children and adults, the early erythematous lesions of PA may be mistaken for psoriasis; however, the distribution, the sparing of scalp, elbows, and knees, and the lack of psoriatic scales exclude this diagnosis.
  • Tinea versicolor
    • The lesions of tinea versicolor favor the upper trunk of adolescents. Potassium hydroxide examination of the associated scale reveals hyphal and yeast forms of Malessia furfur.
  • Vitiligo
    • Vitiligo is an acquired, progressive disorder, in contrast to nevus depigmentosus, which is a stable, congenital leukoderma.
    • The face is a common site for vitiligo, but the distribution is most commonly around the eyes or mouth, and, in contrast to PA, the pigment loss is complete.

Lab Studies:

  • The correct diagnosis is usually suggested by the age of the patient, fine scaling, hypopigmentation, and the distribution of lesions.
  • A potassium hydroxide (KOH) examination may be performed to rule out tinea versicolor, tinea faciei or tinea corporis.

Histologic Findings: Skin biopsy is usually not necessary or particularly helpful in establishing the diagnosis. It may be indicated if the diagnosis of mycosis fungoides (cutaneous T-cell lymphoma) is a significant possibility.

Only a few histologic studies have been reported, most maintain that the microscopic features of PA are those of a chronic, nonspecific dermatitis. Histologic studies reveal features that are suggestive, though not pathognomonic, of the diagnosis. A histopathologic diagnosis of PA may be proposed when the following features are seen in a biopsy specimen taken from a skin lesion with follicular papules:

  • Irregular pigmentation by melanin of the basal layer
  • Follicular plugging
  • Follicular spongiosis
  • Atrophic sebaceous glands

On electron microscopy, there are reduced numbers of active melanocytes and a decrease in number and size of melanosomes in affected skin.

Medical Care:

  • Treatment consists primarily of good general skin care and education of the parents about the benign nature of this self-limited disorder.
  • Hydrocortisone or a bland emollient cream may decrease erythema, scale, and pruritus, if present. For chronic lesions on the trunk, a mild tar paste may be helpful.
  • Patients should use adequate sun protection to prevent darkening of the natural skin color. Lesions of PA do not repigment well upon sun exposure, and darkening of the surrounding skin may worsen the cosmetic appearance.

Consultations:

  • Extensive PA may warrant a dermatology referral for possible oral psoralen and UVA photochemotherapy (PUVA). PUVA for extensive PA may achieve a marked degree of improvement; however, PUVA is not without risks and is seldom required.
  • Consultation with a dermatologist is usually unnecessary; the patient is typically followed by the primary care provider.

Since the disease is usually self-limited and asymptomatic, medical therapy is not always necessary. The most commonly used remedies, including emollients, topical steroids are not always effective.

Drug Category: Corticosteroids, topical -- The low-strength, Class 5 or 6 topical steroids that may be used to treat PA are extremely safe in young children. Prolonged use on the face is not recommended.

Very potent topical steroids may