Epidermal nevi are benign, well-circumscribed proliferations
of the epidermis and papillary dermis appearing in the distribution
of Blaschko’s lines.
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.
Age 80% present in the
first year of life. Most of them appear from birth to 18 years.
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.
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.
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
Type At birth: macular/velvety.
Later: warty/papillomatous plaques. Number Solitary or
Color At birth: white. Later: flesh-colored,
light, or dark-brown. Rarely hypopigmented.
Size Few millimeters to several
Distribution Typically unilateral,
stopping abruptly at midline (Fig. 9-1A). Rarely can be bilateral.
Epidermal nevus A. Brown
whorled verrucous plaques unilaterally on the trunks of an infant. B. Verrucous plaques in a Blashko
line on same infant.
Arrangement Linear following the
lines of Blaschko (Fig. 9-1B).
Sites of Predilection Trunk or
limb > head or neck. Flexural areas are more verrucous.
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).
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)
Epidermal nevi are typically asymptomatic and grow proportionately
with the child. May start macular and become more verrucous ...