A 15-year-old boy is brought in by his mother with a concern about growth of his birthmark. It has become somewhat more raised and bumpy in the past year (Figure 145-1). The adolescent reports no symptoms and is not worried about the appearance. He is otherwise healthy with no neurologic symptoms. The joint decision of the family and the doctor was to not excise the epidermal nevus at this time. He may choose to have this removed by a plastic surgeon in the future.

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  Epidermal nevi (EN) are congenital hamartomas of ectodermal origin classified on the basis of their main component: sebaceous, apocrine, eccrine, follicular, or keratinocytic.

  
  
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  Nevus sebaceous (NS) is a hamartoma of the epidermis, hair follicles, and sebaceous and apocrine glands. A hamartoma is the disordered overgrowth of benign tissue in its area of origin.

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  EN syndrome is also called Solomon syndrome and is a neurocutaneous disorder characterized by EN and an assortment of neurologic and visceral manifestations.

  
  
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  NS is also called sebaceous nevus and nevus sebaceous of Jadassohn (Figure 145-2).

  
  
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  An inflammatory linear verrucous epidermal nevus (ILVEN; Figure 145-3) can be part of an epidermal nevus syndrome but some affected persons only have the cutaneous EN.

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  EN are uncommon (approximately 1 to 3 percent of newborns and children), sporadic, and usually present at birth, although they can appear in early childhood.

  
  
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  EN are associated with disorders of the eye, nervous, and musculoskeletal systems in 10 to 30 percent of patients; in one study, 7.9 percent of patients with EN had one of the nine syndromes—an estimated one per 11,928 pediatric patients.¹

  
  
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  In another review of 131 cases of EN, most (60%) had noninflammatory EN, 1/3 had NS, and 6 percent had inflammatory linear verrucous EN.²

  
  
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  NS are usually present at birth or noted in early childhood.³ Most cases are sporadic but familial cases have been reported.

  
  
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  Linear NS is estimated to occur in 1 per 1000 live births.⁴

  
  
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  Linear NS syndrome includes a range of abnormalities including in the central nervous system (CNS). Patients with CNS involvement typically have cognitive impairment and seizures.⁴ The cardiovascular, skeletal, ophthalmologic, and urogenital systems may also be involved.

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  EN histologically displays hyperkeratosis and papillomatosis, similar microscopically to seborrheic keratosis.³ Also similar to seborrheic keratosis, some ENs of keratinocyte differentiation (about one third) have been found to have a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene.³

  
  
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  Nine EN syndromes have been reported and are described in the referenced article.⁵

  
  
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  ENs frequently have a linear pattern that follows Blaschko lines (Figures 145-1, 145-3, and 145-4), which are believed to represent epidermal migration during embryogenesis.

  
  
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  EN tend to become thicker, verrucous (Figure 145-4), and hyperpigmented at puberty.³

  
  
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  Similarly, NS demonstrate stages of evolution paralleling the histologic differentiation of normal sebaceous glands:⁶

  
  
  
  
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    Infancy and young children—Smooth to slightly papillated, waxy, hairless thickening (Figure 145-5).

    
    
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    Puberty—Epidermal hyperplasia resulting in verrucous irregularity of the surface covered with numerous closely aggregated yellow-to-brown papules (Figure 145-6).

    
    
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    Development of secondary appendageal tumors (Figures 145-7) occurs in 20 to 30 percent of patients, most are benign (most commonly basal cell epithelioma or trichoblastoma), but single (most commonly basal cell carcinoma) or multiple malignant tumors of both epidermal and adnexal origins may be seen and metastases have been reported. Rarely, these malignancies are seen in childhood.

  
  
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  NS were shown to have a high prevalence of human papillomavirus DNA and authors postulate that HPV infection of fetal epidermal stem cells could play a role in the pathogenesis.⁷