This asymptomatic, light-colored patch appeared on a 16-year-old girl’s upper arm 1 month ago. For the past week she has applied a topical antifungal cream, but the lesion remains unchanged.
This lesion is pityriasis alba. The patient has a history of seasonal allergies. Swimming caused low-grade eczema, which interfered with the cells’ ability to pigment normally. The hypopigmentation is accentuated by exposure to the sun because the affected area does not tan.
Dermatophyte infections—as well as psoriasis with its accompanying nail changes—present with more inflammation and scale and have well-defined borders. Vitiligo features depigmentation, not hypopigmentation. The absence of trauma ruled out postinflammatory hypopigmentation.