Pityriasis Alba Workup

Updated: Apr 03, 2020
  • Author: Sarah Sweeney Pinney, MD, FAAD; Chief Editor: Dirk M Elston, MD  more...
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Approach Considerations

Hypopigmentation may occur in other disorders, such as those caused by fungi (eg, tinea versicolor), previous inflammatory conditions (eg, postinflammatory hypopigmentation), idiopathic disorders (eg, vitiligo), or malignancy (mycosis fungoides), or it may occur secondary to medications such as retinoic acid, benzoyl peroxide, and topical steroids. Clinicians should rule out these other disorders when evaluating a patient who may have pityriasis alba.

A workup may be undertaken to exclude other causes of hypopigmentation; however, most of this would be accomplished through a dermatology referral.

A Wood light examination may help in determining whether a patient’s rash is due to vitiligo, which will glow more brightly and have edges with sharper demarcation.

Potassium hydroxide (KOH) stain of a skin scraping will be positive if the patient has tinea versicolor (also called pityriasis versicolor), tinea faciei, or tinea corporis. This would likely be performed by a dermatologist.

A biopsy would be required for atypical lesions noted in the differential. This would likely be performed by a dermatologist.


Histologic Findings

Skin biopsy is not usually necessary or particularly helpful in establishing a diagnosis of pityriasis alba. Biopsy may be indicated, however, if a diagnosis of mycosis fungoides is a significant possibility. The biopsy should be performed by a skin disease specialist, considering the common location of the cheek and the potential approximation of this area to the facial artery.

Only a few histologic studies of pityriasis alba have been reported, and most maintain that the microscopic features of the disease are those of a mild, chronic, nonspecific dermatitis with decreased melanin production. [15, 16, 17, 29] The following features have been seen on biopsy specimens, although none are specific enough to make the diagnosis [2] :

  • Hyperkeratosis (33.33%)

  • Parakeratosis (40%)

  • Acanthosis (53.33%)

  • Spongiosis (80%)

  • Perivascular infiltrate (100%)

However, a histopathologic diagnosis of pityriasis alba may be proposed when the following features are observed in a biopsy specimen taken from a characteristic skin lesion:

  • Irregular or markedly reduced pigment by melanin of the basal layer

  • No significant difference in melanocyte count between lesional and normal skin

  • Reduced number of active melanocytes and decreased number and size of melanosomes in affected skin [12]