Pityriasis Alba Differential Diagnoses
- Author: Sarah Sweeney Pinney, MD; Chief Editor: Dirk M Elston, MD more...
Diagnostic ConsiderationsNevus depigmentosusPigmenting pityriasis albaExtensive pityriasis albaPsoriasisTinea versicolorVitiligoProgressive and extensive hypomelanosisLeprosyMycosis fungoidesDelusional tineaNummular eczema
The differential diagnosis of pityriasis alba includes the following:
Pigmenting pityriasis alba
Extensive pityriasis alba
Progressive and extensive hypomelanosis
Progressive macular hypomelanosis
Eruptive hypomelanosis associated with viral syndromes 
Postinflammatory pigmentary alteration
Ash-leaf macules of tuberous sclerosis
Any inflammatory process that involves the skin, such as contact dermatitis, can leave areas of hypopigmentation upon healing. This may occur in other disorders as well, including fungal diseases (eg, tinea versicolor) and idiopathic disorders (eg, vitiligo), or may result from previous inflammatory conditions (ie, postinflammatory pigmentary alteration).
The most common disorders of hypopigmentation in children are pityriasis alba, vitiligo, nevus depigmentosus, and tinea versicolor.
Hypopigmentation may also result as a adverse effect of medications such as retinoic acid, benzoyl peroxide, and topical steroids.
Nevus depigmentosus is a stable congenital leukoderma. The localized form this condition 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.
Nevus depigmentosus tends to occur on the trunk, is segmental in distribution, and does not change in size or number over time.
This condition seems to be a variant of classic pityriasis alba and shows a strong association with dermatophyte infection, especially tinea capitis. It may be related to lichenoid melanodermatitis. The characteristic morphology of pigmenting pityriasis alba includes a central zone of bluish hyperpigmentation surrounded by a hypopigmented, slightly scaly halo of variable width. Patients display lesions primarily on the face.
Extensive pityriasis alba is differentiated from the classic form by the widespread and symmetrical involvement of the skin, the absence of a preceding inflammatory phase, a higher female-to-male ratio, and, histologically, the absence of spongiosis. Lesions are less erythematous and less scaly in the extensive variant, as well as asymptomatic, more persistent, and more frequently seen on the trunk and less on the face.
In older children and adults, the early erythematous lesions of pityriasis alba may be mistaken for psoriasis; however, the distribution, lack of psoriatic scales, and sparing of scalp, elbows, and knees exclude this diagnosis.
The lesions of tinea versicolor favor the upper trunk of adolescents. Potassium hydroxide examination of the associated scales reveals hyphal and yeast forms of Malassezia furfur.
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 pityriasis alba, the pigment loss is complete.
Widespread cases overlap with a condition termed progressive and extensive hypomelanosis. This disorder occurs mainly in women aged 18-25 years, with progressive development of round, pale, coalescent macules mainly on the back that are unresponsive to therapy but spontaneously regress within 3-4 years.
Leprosy must be considered in arid regions, including areas with armadillo exposure in the United States. In particular, association with the 7-banded armadillo in the southern United States has been described.
This is of particular concern for lesions that are atypical in any way, including lesions that are persistent or symptomatic or that change color or shape
Delusional disorders may result in chronic postinflammatory hypopigmentation changes; it may be possible for such lesions to resemble those of pityriasis alba
This condition is intensely pruritic.
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