Answer: B

Dermal melanocytosis is a clinical spectrum of pigmented lesions characterized by an increased depth and number of melanocytes in the dermis.1 Dermal melanocytosis can be classified by the anatomic location of lesions into subtypes that share similar histopathologic features.2 The most common subtypes include congenital dermal melanocytosis (formerly known as Mongolian spot), nevus fuscoceruleus maxillofacialis (nevus of Ota), and nevus fuscoceruleus acromiodeltoideus (nevus of Ito).1

Congenital dermal melanocytosis is a nonblanching benign birthmark typically found on the lumbosacral and gluteal areas of infants at birth or within the first few weeks of life.2,3 These lesions tend to be irregularly shaped and bluish-green to black in color.3 The pigmentation of the lesions is darkest at age 1 and tends to lighten over approximately 6 years.4 The size of the lesions can range from a few centimeters to more than 20 cm.4

Congenital dermal melanocytosis, which is seen in boys and girls with equal incidence,3  is most commonly found in Asian, black, and Native American populations and is less common in white individuals.3 This racial phenomenon is not well understood, but it has been postulated that the melanocytes of white people contain incompletely melanized melanosomes and that the duration of dermal melanocyte production is more extensive in other races, particularly in Asian individuals.5

Melanocytes arise from neural crest cells and populate the epidermis through migration. In all dermal melanocytosis subtypes, melanocyte migration is believed to be arrested in the dermis, leading to entrapment of melanocytes in this layer of skin.1

Several factors play a role in the color of the lesions, including the amount of melanin within the melanocytes and the number and depth of these melanin-producing cells in the dermis.5 The blue color of the lesions is produced secondary to the Tyndall effect, in which shorter-wavelength colors, such as grey and blue, are reflected to the skin surface by the scattering of light.4 Colors with a longer wavelength, such as red, are not reflected but instead continue deeper into the skin.2

Congenital dermal melanocytosis is thought to be a benign condition without systemic involvement, but recent evidence shows that these lesions may be associated with inborn errors of metabolism and neurocristopathies, which are disorders related to abnormalities in neural crest migration, growth, and differentiation.3,4 Phacomatosis pigmentovascularis is a neurocristopathy that may result in the occurrence of dermal melanocytosis and cutaneous vascular malformations in the same patient.6 The 2 most common lysosomal storage disorders related to inborn errors of metabolism are Hurler syndrome and GM1 (β-galactosidase) gangliosidosis.6 These associations typically are present only when the lesions of congenital dermal melanocytosis are extensively pigmented, persistent, or progressive.6

Histologically, all subtypes of dermal melanocytosis show a sparse melanocytic infiltrate among relatively undisturbed collagen fibers in the dermis.7 These melanocytes are elongated and have thin, pigmented dendrites.7 Under low magnification, the mid-lower dermis shows elongated and spindle-shaped dendritic cells lying parallel to the skin surface.3 At higher magnification, the cells are shown to contain melanin granules and stain positive with Fontana-Masson silver stain.3

The differential diagnosis of congenital dermal melanocytosis includes other dermal melanocytosis subtypes, as well as congenital melanocytic nevus, blue nevus, and potential physical abuse.2

Because nevus of Ota and nevus of Ito share similar clinical and histologic features with congenital dermal melanocytosis, they can be distinguished by the anatomic location of the lesions. Lesions of nevus of Ota appear in areas innervated by the first and second branches of the trigeminal nerve.8 Blue-grey pigmentation of conjunctiva and sclera may be seen, and glaucoma may occur in some cases.3 Lesions of nevus of Ito are located in areas of the skin that are innervated by the posterior subclavian and brachial-cutaneous nerves.7 Both nevi may occur separately or in conjunction with one another and extensive types of congenital dermal melanocytosis.3 Unlike the lesions of congenital dermal melanocytosis, nevus of Ito and nevus of Ota do not spontaneously regress during childhood and may even darken with age.1

Congenital melanocytic nevus is another pigmented lesion caused by abnormal proliferative capacity and migration of melanocytes.9 Lesions typically are dark brown in color. They are papillated or verrucous on the surface and occasionally can be keratotic.7 The lesions can change in color and develop overlying hair.9 It is imperative to distinguish congenital melanocytic nevus from other lesions due to its association with neurocutaneous melanocytosis, melanoma, and psychosocial impairment.9

Blue nevus is another pigmented lesion that often presents in the second decade of life but occasionally can be congenital.3 Common blue nevus appears as a bluish-black macule, papule, or plaque.10 The most common locations for these lesions are the head, neck, presacral area, and distal extremities.10 These lesions are much smaller than those of congenital dermal melanocytosis, commonly measuring <1 cm in diameter.4

The lesions of congenital dermal melanocytosis may be mistaken for bruises from physical abuse, especially if they present in unusual locations. The lesions are distinguished from bruises by the absence of tenderness, a lack of color change or evolution with time, and a time period of several months to years for the lesion to disappear.2 

The diagnosis of congenital dermal melanocytosis is made clinically largely based on onset, location, and evolution of the lesions, with assistance from analysis of biopsy specimens.4 Because the lesions of congenital dermal melanocytosis typically resolve by early childhood, no treatment is necessary if they are located in the typical lumbosacral region. If the lesions are extrasacral, large, or extensively pigmented, Q-switched alexandrite lasers (755 nm) can be used to lighten the lesion.4 However, persistent lesions may indicate the presence of the aforementioned systemic complications and the patient should be examined for such. 

For the patient in our case, clinical presentation and biopsy of the lesion were consistent with congenital dermal melanocytosis. Because the lesion was typical in presentation, no treatment was initiated. The patient was observed, and the lesion regressed over the following year. There were no complications.

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