Chapter 164. Epidermal Nevus and Nevus Sebaceous

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 164-1). 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.

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

• EN syndrome is also called Solomon syndrome and is a neurocutaneous disorder characterized by EN and an assortment of neurologic and visceral manifestations.
• NS is also called sebaceous nevus and nevus sebaceus of Jadassohn (Figure 164-2).
• An inflammatory linear verrucous epidermal nevus (ILVEN) (Figure 164-3) can be part of an epidermal nevus syndrome but some affected persons only have the cutaneous EN.

• EN are uncommon (approximately 1% to 3% of newborns and children), sporadic, and usually present at birth, although they can appear in early childhood (Figure 164-4).
• EN are associated with disorders of the eye, nervous, and musculoskeletal systems in 10% to 30% of patients; in one study, 7.9% of patients with EN had 1 of the 9 syndromes—an estimated 1 per 11,928 pediatric patients.1
• In another review of 131 cases of EN, most (60%) had noninflammatory EN, one third had NS, and 6% had ILVEN.2
• NS is usually present at birth or noted in early childhood (Figure 164-5).3 Most cases are sporadic but familial cases have been reported.2
• Linear NS is estimated to occur in 1 per 1000 live births.4
• Linear NS syndrome includes a range of abnormalities, including the central nervous system (CNS); patients with CNS involvement typically have cognitive impairment and seizures3; other organ systems, including the cardiovascular, skeletal, ophthalmologic, and urogenital systems, may be involved.

• EN histologically display hyperkeratosis and papillomatosis, similar microscopically to seborrheic keratosis (see Chapter 158, Seborrheic Keratosis).2 Also similar to seborrheic keratosis, some EN of keratinocyte differentiation (approximately one third) have been found to have a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene.
• Nine EN syndromes have been reported and are described in the referenced article.5
• EN frequently have a linear pattern that follows Blaschko lines (Figures 164-1, 164-3, and 164-4), which are believed to represent epidermal migration during embryogenesis.
• EN tend to become thicker, verrucous (Figure 164-4), and hyperpigmented at puberty.2
• Similarly, NS demonstrates stages of evolution paralleling the histologic differentiation of normal sebaceous gland:6
  • Infancy and young children—Smooth to slightly papillated, waxy, hairless thickening (Figure 164-5).
  • Puberty—Epidermal hyperplasia resulting in verrucous irregularity of the surface covered with numerous closely aggregated yellow-to-brown papules (Figure 164-6).
  • Development of secondary appendageal tumors (Figures 164-7 and 164-8) occurs in 20% to 30% 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.2 Rarely, these malignancies are seen in childhood.
• NS was shown to have a high prevalence of human papillomavirus DNA and authors postulate that human papillomavirus (HPV) infection of fetal epidermal stem cells could play a role in the pathogenesis.7

Making the Diagnosis

Clinical features of EN

• EN are linear, round, or oblong; well-circumscribed; elevated; and flat-topped (Figures 164-1 and 164-4).
• Color is yellow-tan to dark brown.
• Surface is uniform velvety or warty (Figures 164-4 and 164-5).
• ILVEN, a less common type of EN, is pruritic and erythematous (Figure 164-3).

Clinical features of NS

• NS has an oval to linear shape ranging from 0.5 × 1 cm to 7 × 9 cm.
• NS is usually a solitary, smooth, waxy, hairless thickening noted on the scalp at birth or in early childhood (Figures 164-2 and 164-6).
• Early NS may be pink, orange, yellow, or tan; later lesions can appear verrucous and nodular (Figure 164-5).

Typical Distribution

• EN occur most commonly on the head and neck followed by the trunk and proximal extremities; only 13% have widespread lesions (Figure 164-9). Lesions may spread beyond their original distribution with age.
• NS are commonly found on the scalp followed by forehead and retroauricular region (Figures 164-2 and 164-5, 164-6, 164-7, and 164-8) and rarely involves the neck, trunk, or other areas.

Biopsy

• Biopsy is the most definitive method for diagnosing these nevi. A biopsy is not needed if the clinical picture is clear and no operative intervention is planned. A shave biopsy should provide adequate tissue for diagnosis because the pathology is epidermal and in the upper dermis.
  • Histologic features of epidermolytic hyperkeratosis within an EN are associated with mutations in the keratin gene that may be transmitted to offspring; widespread cutaneous involvement may be seen.2

• Linear lichen planus (Figure 164-10)—Discrete, pruritic, violaceous papules are arranged in a linear fashion, usually extending along an entire limb.
• Syringoma (Figure 164-11)—Benign adnexal tumor derived from sweat gland ducts. Autosomal dominant transmission, soft, small, skin-colored to brown papules develop during childhood and adolescence, especially around the eyes, but may be found on the face, neck, and trunk.
• Lichen striatus—Discrete pink, tan, or skin-colored asymptomatic papules in a linear band that suddenly appear. The papules may be smooth, scaly, or flat topped. It is mostly seen in children. Although it is most commonly seen on an extremity, it can appear on the trunk (Figure 164-12). It can resemble a linear EN but lichen striatus will spontaneously regress within 1 year.
• Linear porokeratosis—Characterized by small, annular, hypertrophic verrucous plaques with a linear morphology usually limited to a single extremity. The annular morphology and dermatomal distribution should help distinguish this condition from EN and NS.

Medications

• There are no proven topical methods for treatment of these lesions. Topical retinoids may improve lesion appearance but recurrence is common.2

Procedures

• Destructive modalities for EN, such as electrodessication and cryotherapy, may temporarily improve the appearance of the lesion, but recurrence is frequent.2
• Carbon dioxide laser is an alternative option for EN; however, scarring and pigment changes are potential permanent complications, especially in patients with darker skin types.8 This treatment does not completely remove NS and there is recurrence risk.2
• Surgical excision is an option that may be complicated by scarring.
• Because of the potential for malignant transformation particularly following puberty, some authors recommend early complete plastic surgical excision for NS; SOR C reconstructive surgery may be needed.
• Excision of large lesions may require reconstructive surgery with a rotation flap to close.9

• There are reports of spontaneous improvement in patients with widespread involvement of EN.
• Malignant potential is low in EN.2
• Malignant potential in NS is uncertain. Reports range from 0% to 2.7%.2
  • Early reports suggested a high rate of developing basal cell carcinomas, whereas more recent studies identified trichoblastoma and syringocystadenoma papilliferum in NS, usually in adulthood.2
  • In a retrospective analysis of 757 cases of NS from 1996 to 2002 in children age 16 years or younger, investigators found no malignancies and question the need for prophylactic surgical removal.10
  • Squamous cell carcinoma has also been described in a NS.11

• Patients with NS should be examined for other associated findings. Consider a consultation with a neurologist and/or ophthalmologist.
  • In a study of 196 subjects with NS examined for clinical neurologic abnormalities, only 7% had abnormalities.12 Abnormal exams were more frequent in individuals with extensive nevi (21% vs. 5%) and a centrofacial location (21% vs. 2%). The patients depicted in this chapter had no neurologic abnormalities.

Patient Resources

• Nevus Outreach. Other Kinds of Nevi—http://www.nevus.org/other-kinds-of-nevi_id559.html.
• Genetics Home Reference. Epidermal Nevus—http://ghr.nlm.nih.gov/condition/epidermal-nevus.

Provider Resources

• Medscape. Nevus Sebaceous—http://emedicine.medscape.com/article/1058733-overview.
• Medscape. Epidermal Nevus Syndrome—http://emedicine.medscape.com/article/1117506-overview.