CASE #1: Epidermal nevus

Epidermal nevus is also known as nevus verrucosus, nevus unius lateris and ichthyosis hystrix. The word nevus is derived from Latin and has three different meanings. The first of these meanings is a harmartoma, which means a focal benign growth resembling a neoplasm that develops with an excess or deficiency of structural elements that are normally found in the affected area. The second meaning is a benign tumor of melanocytes. The final meaning is a congenital lesion or a lesion that arises early in life — essentially a birthmark.1

An epidermal nevus is considered a hamartoma of the epidermis and papillary dermis. The two forms of epidermal nevus are the nonorganoid and the organoid versions. The latter consists of nevus sebaceus and follicular nevi. The former consists of keratinocytic nevi. 

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Approximately one of every 1,000 infants will develop an epidermal nevus. The disease affects all racial backgrounds and genders equally. Prevalence studies have determined that epidermal nevus develops sporadically, although there have been familial cases.2,3 The age of onset ranges from birth to approximately age 14 years; however, roughly 80% of cases occur before the first year of life.4

Epidermal nevi arise from the embryonic epidermis, particularly from pluripotential germinative cells in the basal layer. Mosaicism was thought to be the cause of most epidermal nevi, and until recently, only nevi histologically associated with acantholytic dyskeratosis and epidermolytic hyperkeratosis had been proven to be due to genetic mosaicism.5 More recently, fibroblast growth factor receptor 3 was found to have mosaicism for activating mutations in those with “common” epidermal nevi.5

There is a risk of various malignancies developing within an epidermal nevus, with most of them occurring after puberty. These include such neoplasms as basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and keratoacanthoma. 

Epidermal nevi usually present as a single linear lesion; however, they may be seen as multiple linear plaques or have a bilateral distribution. The nevi often follow Blaschko’s lines (lines that trace the migration of embryonic cells) and are most commonly seen on the trunk, neck and extremities. Blaschko’s lines will appear in a wavy or V-shaped pattern on the trunk and in a linear pattern on the extremities. The lesions are generally hyperpigmented, well-circumscribed papillomatous papules and plaques that are asymptomatic. Once the growth of the plaque stabilizes, it may become thicker over time, especially in such flexural regions as the neck and joints. 

Nevus verrucosus is a localized form of epidermal nevus. The plaques of this nevi tend to be very warty in appearance. When lesions appear extensive, unilateral, and often involve the trunk, it is termed nevus unius lateris. Systematized epidermal nevus, also known as ichthyosis hystrix, is a variant with extensive bilateral involvement.6

Epidermal nevus with a combination of such developmental abnormalities as mental retardation, central nervous system abnormalities, and/or musculoskeletal abnormalities could be a good indicator of epidermal nevus syndrome.5,7 A study that evaluated 119 patients with epidermal nevi found that approximately 33% of participants had one organ-system abnormality, approximately 6% had two organ systems with abnormalities, 5% had three organ-system abnormalities, and 5% with five or more organ system abnormalities.5 A thorough history and physical examination should be performed at the time of presentation to rule out any systemic involvement. 

A biopsy and histologic examination of an epidermal nevus will reveal hyperkeratosis, papillomatosis, and acanthosis with rete ridge elongation in a psoriasiform pattern.8 Such other findings as epidermolytic hyperkeratosis and acantholytic dyskeratosis may also be seen. Evaluation for the presence of neoplasms such as BCC, SCC, and keratoacanthoma should ensue. 

There are many nevoid conditions that are distributed along Blaschko’s lines that must be differentiated from an epidermal nevus. These include such disorders as porokeratotic eccrine ostial and dermal duct nevus, linear lichen planus and X-linked dominant chondrodysplasia punctata.5