DISCUSSION
This phenomenon is so common in dermatology clinics that it’s a rare day when we don’t see it. This form of hypopigmentation is pityriasis alba (PA), in which areas of eczema don’t tan at all while the surrounding skin darkens with sun exposure. The lateral aspects of the arms are often affected (sparing the sun-protected medial aspects), as are the sides of the face and the posterior neck. The contrast is striking, especially on those with darker skin.
PA occurs mostly in children and young adults, becoming less frequent with age. It differs from vitiligo in that PA involves seasonal, partial pigment loss; vitiligo by contrast manifests with complete pigment loss (leaving utterly white skin) that is almost always permanent.
Treatment consists of sun protection, moisturization to prevent eczema, and use of class IV steroid creams or ointments when lesions appear. Even without treatment, PA usually clears during the winter months—when the surrounding skin loses its tan—only to recur the following spring.
TAKE-HOME LEARNING POINTS
- Pityriasis alba (PA) occurs when patches of eczema fail to tan, producing marked contrast between them and the normal surrounding skin; it is often mistaken for fungal infection.
- PA favors the antecubital, deltoid, and lateral tricep areas, as well as the lateral face.
- PA is more common in atopic individuals who are prone to eczema and appears more dramatic in those with darker skin.
- Vitiligo is a major item in the differential, but color loss with PA is only partial (rather than permanent) and almost always resolves in the winter.
- Once color is lost with PA, treatment is largely ineffective. It is then best to use preventive measures (eg, sunscreen and moisturizer), plus/minus topical steroid creams, for the eczema.