A Distressing Diagnosis
A 12-year-old black girl presents with hypopigmented patches on her cheeks and upper arms that appeared in the past month. The discoloration was sudden in onset and noticed shortly after a trip to Bermuda, prompting evaluation by her pediatrician, who diagnosed vitiligo. The parents are extremely distressed, because they were told vitiligo is an autoimmune, lifelong disease that may worsen over time and has no effective treatment. They read about the condition online and came in for a dermatologic consultation, requesting "laser treatment" to stimulate repigmentation. The girl's medical history is significant for "sensitive skin" with childhood flexural eczema and paternal asthma. The examination reveals a healthy-appearing girl with Fitzpatrick skin phototype V and ill-defined, hypopigmented, slightly scaly patches on her cheeks and upper arms that do not enhance with Wood's lamp evaluation. KOH scraping is negative. She also has perifollicular hypopigmentation with a rough texture on her upper arms consistent with keratosis pilaris.
What is the medical diagnostic error in this case?
The Cause of Hypopigmentation
This girl has pityriasis alba, a common variant of atopic dermatitis that typically presents in young children with darker skin phototypes. These asymptomatic or mildly pruritic patches are caused by postinflammatory hypopigmentation, classically on the cheeks and upper arms. As in this case, pityriasis alba is most prominent in the summer or following heavier sun exposure and gradually disappears with time. Although no treatment is needed, emollients and low-potency topical corticosteroids may speed resolution.
In contrast, vitiligo is a chronic pigmentary disorder caused by destruction of melanocytes and characterized by well-demarcated white macules and patches with scalloped borders and variable follicular sparing (speckling), often occurring in areas of friction (Koebner phenomenon) (Figure 4).
Patches of vitiligo enhance under Wood's lamp illumination, whereas skin affected by pityriasis alba does not. Vitiligo affects up to 1% of the population; is associated with thyroid disease, alopecia areata, and diabetes mellitus; and is notoriously difficult to treat but may improve with topical corticosteroids, topical calcineurin inhibitors, or phototherapy (narrowband UVB light, psoralen and UVA light, excimer laser).
The differential diagnosis for acquired hypopigmented patches in children includes pityriasis versicolor (truncal distribution with pink to hyper- or hypopigmented patches showing a positive "spaghetti-and-meatballs" appearance on KOH scraping; Figure 5).
Other conditions that should be considered include pityriasis lichenoides chronica, chemical leukoderma, leprosy (in endemic areas), and hypopigmented mycosis fungoides. This latter diagnosis, although rare, is a primary cutaneous lymphoma that may mimic pityriasis and is often misdiagnosed. Hence, a skin biopsy should be performed if hypopigmentation is refractory to emollient therapy, progressive, widespread (eg, torso and extremities), or associated with cutaneous atrophy or central "lacy" erythema.
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Cite this: Diagnostic Errors in Patients With Rashes, Moles, and Other Skin Findings - Medscape - Sep 06, 2017.