Epidermal Nevus

The term epidermal nevus (EN) is applied to a variety of congenital hamartomas that are composed of cells derived from the embryonic ectoderm.
Epidermal nevi are categorized based on the predominant ectodermal cell type present. For example, an NS is a type of EN, so named because sebaceous glands predominate (see earlier in this chapter).
Keratinocytic epidermal nevi (composed mostly of keratinocytes) are the most common type of EN and are the type that is discussed here.

Pathogenesis ⬆ ⬇

Epidermal nevi reflect cutaneous mosaicism and are thought to result from a somatic mutation in a single ectodermal cell that then gives rise to a clone of genetically identical cells (see below).

Clinical Manifestations ⬆ ⬇

The clinical appearance of EN is variable.
EN are often seen as a variably sized linear plaque(s) along the lines of Blaschko which represent the embryonic migration of skin cells.
EN can be skin-colored to pink or hyperpigmented and flat or slightly raised (Fig. 1.29).
EN are typically localized but can be widespread (Fig. 1.30).
EN can be present at birth or appear in infancy or early childhood.
Initially lesions are flat or slightly raised and over time, some lesions thicken and can become warty.
EN are usually an isolated finding but occasionally, especially large and extensive EN, can be associated with an underlying syndrome or extracutaneous defect.

Diagnosis ⬆

Diagnosis is usually made clinically.
A skin biopsy may occasionally be necessary to determine subtype of EN or to differentiate an EN from an inflammatory skin condition such as psoriasis.

Differential Diagnosis

Hyperpigmented Pigmentary Mosaicism (aka Segmental Pigmentation Disorder; see Fig. 1.34)

Linear and whorled hyperpigmented streaks present at birth and remain stable and flat over time.

Psoriasis

Occasionally psoriasis may present in a linear or segmental distribution and can be mistaken for an EN.
Psoriasis will be pink-red with overlying silvery white scale and responds to topical steroids.

Lichen Striatus

Long, linear plaque composed of flat-topped papules commonly seen on the extremities in children.
Not present at birth and spontaneously resolve over months to years.

Verruca Vulgaris

Management

Patients with large or extensive EN require a thorough medical and family history and physical evaluation with particular attention to the neurologic, ocular, and cardiovascular systems. A symptom-directed workup should be performed as necessary.
Most EN lack associated defects and are only of cosmetic concern.
Because most EN thicken and become warty over time, many patients request complete removal or destruction.
Method of treatment depends on size and location of the lesion. Surgical excision will provide the most definitive result for most small, localized lesions.
Larger lesions are often treated with a combination of superficial destructive and surgical methods.
Superficial destructive methods such as cryotherapy, electrodessication, and laser ablation have variable results and are often followed by recurrence.
Ablative CO₂ laser therapy and Fraxel laser are effective in removing EN.
Topical therapies such as topical retinoids, 5-fluorouracil and topical corticosteroids can improve the appearance of the EN in some cases.