Chapter 43: Epidermal Nevus

INTRODUCTION

Epidermal nevus (EN) is a benign hamartomatous growth. It presents as a group of verrucous, closely grouped, skin-colored to brown papules often in a linear arrangement following the Lines of Blaschko (Fig. 43.1). It develops primarily in childhood. There are several variations of EN including localized nevus unius lateris, systematized EN, EN syndrome, and inflammatory verrucous epidermal nevus (ILVEN) (Fig. 43.2).

EPIDEMIOLOGY

Incidence: 0.1% of births

Age: majority in the first year of life; few develop in puberty

Race: none

Sex: female predominance in ILVEN

Precipitating factors: usually sporadic; familial cases reported

PATHOGENESIS

EN is created by overproduction of keratinocytes from pluripotent embryonic epidermal basal keratinocytes. Genetic mosaicism is thought to be responsible for most epidermal nevi.

PATHOLOGY

Papillomatosis, acanthosis, epidermal hyperplasia, and hyperkeratosis along with elongated rete ridges are present. In some lesions, epidermolytic hyperkeratosis and variable parakeratosis may be present. If this finding is made in the setting of multiple epidermal nevi, genetic counseling should be offered in order to educate patients as to the risk of epidermolytic hyperkeratosis in offspring. Neoplasms such as keratoacanthoma, basal cell carcinoma, and squamous cell carcinoma may rarely develop in association with epidermal nevi.

PHYSICAL LESIONS

Commonly present as a single linear lesion, although unilateral or bilateral linear plaques may be present. Most consist of multiple, well-defined, closely grouped linear, yellow, pink, or brown verrucous papules on any body site. EN often follows the Lines of Blaschko on the trunk and travels longitudinally on the extremities. Size can vary from a few millimeters to multiple centimeters. May thicken and become more verrucous over time, especially in flexural regions. Erythema is a common feature of ILVEN.

DIFFERENTIAL DIAGNOSIS

Nevus sebaceous, seborrheic keratosis, verruca vulgaris, lichen striatus, melanocytic nevus, lichen planus, psoriasis.

LABORATORY EXAMINATION

A biopsy may be indicated to distinguish from nevus sebaceous or lichen striatus. Rarely, basal cell and squamous cell carcinoma may arise in EN.

COURSE

An EN generally presents at birth or childhood as macules initially which thicken over time. Eighty percent of ENs appear within the first year of life. At puberty, they tend to enlarge, darken, and become more verrucous. ILVEN may be pruritic in nature.

KEY CONSULTATIVE QUESTIONS