Derm Dx: A darkening, thickening birthmark

Epidermal nevi are lesions originating from the pluripotent cells in the basal layer of the epidermis. The lesions can be congenital (i.e. a type of  "birthmark") or may appear early in life. Male and female patients are equally affected. The...

Submit your diagnosis to see full explanation.

Epidermal nevi are lesions originating from the pluripotent cells in the basal layer of the epidermis. The lesions can be congenital (i.e. a type of  “birthmark”) or may appear early in life. Male and female patients are equally affected. The pathogenesis behind all types of epidermal nevi is thought to be mosaicism with genetic mutations within the affected skin.

Epidermal nevi can be classified by the epidermal cells from which it derives – it is not uncommon to find elements of various cell types within the same epidermal nevus.

Epidermal nevi that arise from keratinocytes, the predominant cells within the epidermis, are referred to as keratinocytic epidermal nevi, or nonorganoid epidermal nevi. In contrast, organoid epidermal nevi arise from non-keratinocytic epidermal cells. Nevus sebaceous is one example of an organoid epidermal nevus that arises from the sebaceous glands within the epidermis.

A keratinocytic epidermal nevus most commonly presents as a single linear lesion of skin-colored, dirty-grey, or brown papule which coalesces to form a serpiginous plaque following Blaschko lines with a possible abrupt midline demarcation.

Most lesions are well-circumscribed and asymptomatic. Horny excrescences may be interspersed within the localized patch. Once developed, the nevi may thicken and become verrucous. Epidermal nevi most commonly occur on the trunk, extremities, or the neck. The size and distribution of nevi are highly variable.

Nevus sebaceous is a subtype of epidermal nevus with hamartomatous components of sebaceous glands accompanying the papillomatous epidermis. This subtype presents as a sharply circumscribed, solitary, linear, yellow-orange lesion on the scalp or head and neck. The lesion persists throughout life and is usually alopecic. The lesion begins papillated and velvety, but as the sebaceous elements undergo hyperplasia in adulthood, the lesion becomes elevated and cerebriform.

Numerous neoplasms including basal cell carcinoma, squamous cell carcinoma, and keratoacanthomas, have been described as arising in sebaceous nevi. The risk of tumor development increases with age.

The histological pattern of epidermal nevi varies, and more than 10 frequently overlapping patterns have been described. However, all epidermal nevi are characterized by epidermal hyperplasia, hyperkeratosis (thickening of the stratum corneum), acanthosis (thickening of the basal layer of the epidermis), papillomatous, and variable parakeratosis (retention of nuclei in the stratum corneum).

In general, larger and more widespread epidermal nevi and lesions of the head and neck are more likely to be associated with internal complications.

The combination of epidermal nevi and internal organ involvement is termed epidermal nevus syndrome. These abnormalities most commonly involve the neurologic or musculoskeletal system.

One example is Schimmelpenning syndrome, in which sebaceous nevi are associated with colobomas of the eye, cerebral defects, and skeletal defects secondary to vitamin D resistant hypophosphatemic rickets. Another example is angora hair nevus syndrome, in which a linear epidermal nevus covered with long white hair is coupled with central nervous system, eye and skeletal abnormalities.

Young children with multiple and extensive epidermal nevi require a thorough history and physical to evaluate for possible systemic abnormalities.

Full-thickness surgical excision is curative, but recurrence is common when only the epidermis is removed because some epidermal nevi involve some portion of the superficial dermis.

Oral retinoids and laser ablations may also be effective, but retinoids fail to provide complete resolution and lasers may result in fibrosis and scarring that is cosmetically unacceptable to patients.

Nevus Anemicus

Nevus anemicus is a congenital vascular anomaly that results in pale areas of the skin. It presents as macules of varying size and shape with an irregular border that are paler than the surrounding skin and cannot be made red by trauma, cold, or heat.

Nevus anemicus is most commonly found on the upper to mid trunk. The nevus may resemble vitiligo, but there is a normal amount of melanin in the lesion. On physical exam, light does not accentuate the lesion and diascopy or application of pressure causes the borders and extent of the lesion to become imperceptible due to blanching of surrounding skin.

Application of heat or ice accentuates the lesion by creating an increasingly hyperemic border while the lesion remains pale. The underlying pathogenesis is an increased sensitivity of blood vessels to catecholamines with permanent vasoconstriction.

Nevus anemicus is differentiated from vitiligo by the pale appearance of the lesion as opposed to the absence of pigmentation and by using the physical exam signs noted previously.  Nevus anemicus does not require treatment, and no treatment is effective.

Halo Nevus

Halo nevus is characterized by a nevus surrounded by a ring of depigmentation or “halo.” It is typically found in patients aged 20 years and younger and is associated with an increased number of melanocytic nevi and an increased predilection for vitiligo.

The most commonly accepted pathogenesis behind halo nevi is an immune response against altered melanocytic nevus resulting in surrounding destruction of melanocytes and the formation of the halo.

Histologically, the central nevus demonstrates infiltrates of lymphocytes and histiocytes while the outer halo demonstrates complete absence of melanocytes.

After development of halo nevi, the course is variable. In most patients, the nevus loses its pigmentation and disappears leaving a white macule. In rare cases however, the central nevus can persist indefinitely with repigmentation of the halo.

The most important task of the clinician is to distinguish halo nevi from melanomas, which sometimes also present with a halo, though the halo is often more asymmetric than the halo of a halo nevus.

Nevus Depigmentosus

Nevus depigmentosus is a hypopigmented skin condition that is thought to reflect cutaneous mosaicism.  The most common presentation of nevus depigmentosus is a localized patch with smaller macules at the edges of the lesion that is said to resemble a splash of paint.

Although lesions of depigmentosus are classically present at birth, they may sometimes become apparent later in childhood in individuals with lighter skin.

Christopher Chu is a medical student at Baylor College of Medicine.  

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine also in Houston.

1. Bolognia J, Jorizzo J, Rapini R. 2008. “Chapter 62 – Mosaicism and Linear Lesions.” Dermatology. St. Louis, MO: Mosby/Elsevier. Print.
2. Bolognia J, Jorizzo J, Rapini R. 2008. “Chapter 109 – Benign Epidermal Tumors and Proliferations.” Dermatology. St. Louis, MO: Mosby/Elsevier. Print.
3. Bolognia J, Jorizzo J, Rapini R. 2008. “Chapter 112 – Benign Melanocytic Neoplasms.” Dermatology.  St. Louis, MO: Mosby/Elsevier. Print.
4. William J, Berger T, Elston D, Odom R. 2006. “Chapter 28 – Dermal and Subcutaneous Tumors.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunder Elsevier. Print.
5. William J, Berger T, Elston D, Odom R. 2006. “Chapter 29 -Epidermal Nevi, Neoplasms, and Cysts.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunder Elsevier. Print.
6. William J, Berger T, Elston D, Odom R. 2006. “Chapter 30 – Melanocytic Nevi and Neoplasms.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunder Elsevier. Print.