An 8-year-old patient presents for a routine physical exam. His mother notes a white patch of skin that she states has been present since the boy was several weeks old. The patient has an otherwise normal exam.
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This patient was diagnosed with nevus depigmentosus, a hypopigmented skin condition that is thought to reflect cutaneous mosaicism. The most common presentation of nevus depigmentosus is a localized hypopigmented patch with smaller macules at the periphery of the lesion that is said to resemble a splash of paint.
Although lesions of nevus depigmentosus are usually present at birth, the condition may sometimes become apparent later in childhood among patients with lighter skin. Telling patients they have a “white birthmark,” makes the condition easy for them to understand.
Nevus anemicus is a congenital vascular anomaly that results in pale areas of the skin. It presents as macules of varying size and shape with an irregular border that is paler than the surrounding skin and cannot be made red by trauma, cold, or heat.
Nevus anemicus is most commonly found on the upper to mid trunk. The nevus may resemble vitiligo, but there is a normal amount of melanin in the lesion. Diascopy or application of pressure causes the borders and extent of the lesion to become imperceptible due to blanching of surrounding skin.
The underlying pathogenesis is increased blood vessel sensitivity to catecholamines with permanent vasoconstriction. Nevus anemicus does not require treatment and no treatment is effective.
Epidermal nevi usually present as a single, linear lesion of well-circumscribed hyperpigmented, papillomatous papules or plaques that are usually asymptomatic.
The lesions most typically occur on the trunk, extremities or the neck, and the distribution of the nevi are highly variable.
Epidermal nevi follow the lines of Blaschko, suggesting a postzygotic mutation as the underlying pathophysiology.
Halo nevi are characterized by a nevus surrounded by a ring of depigmentation or “halo.”
The most commonly accepted pathogenesis behind halo nevi is an immune response against altered melanocytic nevus resulting in surrounding destruction of melanocytes and the formation of the halo.
Christopher Chu is a medical student at Baylor College of Medicine.
Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine also in Houston.
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