Section 9. Benign Epidermal Proliferations

Epidermal nevi are benign, well-circumscribed proliferations of the epidermis and papillary dermis appearing in the distribution of Blaschko’s lines.

Insight

When examining a lesion that appears linear, consider the swirled or undulating pattern of Blaschko’s lines; if present, this will immediately focus the differential diagnosis.

Synonyms Nevus verrucosus, nevus unius lateris, ichthyosis hystrix, and linear nevus sebaceus.

Epidemiology

Age 80% present in the first year of life. Most of them appear from birth to 18 years.

Gender M = F.

Prevalence 1 in 1000 infants.

Etiology Most cases sporadic, some cases familial. Mutations in gene for fibroblast growth factor receptor 3 (FGFR3) identified. Some exhibit a chromosomal break at 1q23.

Pathophysiology

Epidermal nevi arise from the pluripotent embryonic basal cell layer. There are likely many different candidate gene mutations that result in epidermal nevi, but only FGFR3, PTEN, and epidermal differentiation genes at 1q23 have been suggested thus far.

History

Epidermal nevi are present at or soon after birth. Solitary small lesions are common. Larger lesions can affect an entire limb or side of the body with associated adnexal tissue proliferations or hypertrophy.

Physical Examination

Skin Findings

Type At birth: macular/velvety. Later: warty/papillomatous plaques. Number Solitary or multiple.

Color At birth: white. Later: flesh-colored, light, or dark-brown. Rarely hypopigmented.

Size Few millimeters to several centimeters.

Distribution Typically unilateral, stopping abruptly at midline (Fig. 9-1A). Rarely can be bilateral.

Arrangement Linear following the lines of Blaschko (Fig. 9-1B).

Sites of Predilection Trunk or limb > head or neck. Flexural areas are more verrucous.

Differential Diagnosis

The diagnosis of an epidermal nevus is made based upon history and physical examination. The differential diagnosis includes linear and whorled hypermelanosis, nevus sebaceus, seborrheic keratosis, wart, psoriasis, lichen striatus, incontinentia pigmenti, hypomelanosis of Ito, or an inflammatory linear verrucous epidermal nevus (ILVEN).

Laboratory Examinations

Dermatopathology Skin biopsy shows epidermal hyperplasia, hyperkeratosis, acanthosis, papillomatosis, and parakeratosis. There may be increased melanin in the basal layer in places. There may be ballooning of the cells (epidermolytic hyperkeratosis) in places.

Course and Prognosis

Epidermal nevi are typically asymptomatic and grow proportionately with the child. May start macular and become more verrucous ...