Pityriasis alba is a common condition primarily affecting children, but not exclusively, and especially those with atopic diathesis (eg, asthma, allergic rhinitis and conjunctivitis, atopic dermatitis). It is characterized by hypopigmented macules or patches. Lesions may be asymptomatic or mildly pruritic and range in size from 0.5-5 cm. Classically, there is no preceding inflammatory stage, and, on examination, fine scale may be present. Often, the lesions are poorly demarcated; however, at times, the hypopigmentation may be well defined. The disorder is associated with dry skin (xerosis).
Pityriasis alba often has a chronic course, tends to relapse, and usually worsens in the summer with increased sun exposure. It predominately occurs in children between the ages of 3 and 16 years and is found equally in both sexes. In the majority of patients, spontaneous resolution typically occurs before adulthood. Lesions most commonly occur on the face and upper arms. This disorder is common in all ethnicities, although the hypopigmented lesions are more obvious in patients with darker skin phototypes.
The exact cause of the condition is unknown, although the characteristic hypopigmentation may be secondary to a preceding subclinical dermatitis. Environmental triggers such as heat, humidity, sunlight exposure, detergents / soaps, abrasive clothing, chemicals, and smoke, along with stress, may aggravate this disorder. Microorganisms such as Pityrosporum, Streptococcus, Aspergillus, and Staphylococcus may also be triggers. Evidence also suggests that pityriasis alba is a mild eczematous dermatitis.
Codes
ICD10CM: L30.5 – Pityriasis alba
SNOMEDCT: 402296004 – Pityriasis alba
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Differential Diagnosis & Pitfalls
Extensive cases may resemble the hypopigmented form of tinea versicolor, especially if hypopigmentation involves the face.
In vitiligo, the patches are completely depigmented and very well demarcated.
Unlike pityriasis alba, tinea corporis usually has raised borders.
Topical medication such as retinoic acid, benzoyl peroxide, and potent topical steroids may present in a similar fashion.
Psoriasis usually has a thicker scale and a more well-defined border than pityriasis alba.
Atopic dermatitis – Pityriasis alba may be a manifestation of postinflammatory hypopigmentation, seen in individuals with atopic dermatitis.
Although similar, seborrheic dermatitis is less commonly seen in preschoolers and school-aged children.
Nummular dermatitis is usually more well defined, the lesions are raised with more prominent scale, and there is intense pruritus.
Tuberous sclerosis usually includes hypopigmented patches on the trunk and presents at birth with associated seizure, intellectual disability, and other skin lesions; shagreen patches and angiofibromas.
