Dermal Melanocytosis

Etiology

Congenital dermal melanocytosis occurs from improper migration or clearance of melanocytes from the dermal layer during fetal development.[1]  There are currently no preventable factors that have been cited to affect congenital dermal melanocytosis. However, recent data support an association of aberrant congenital dermal melanocytoses with inborn errors of metabolism.[2] 

Epidemiology

In congenital dermal melanocytosis, both sexes are equally affected.[2] Most patients are affected at birth or shortly after birth, with a majority of cases having the lesions disappear by 1 year old, rarely persisting after 6 years old.[3][4]

However, the prevalence is affected by population ethnicity, with the highest prevalence occurring in Asian and Black populations.[5] Multiple studies have demonstrated similar ranges in prevalences by ethnicity, as listed below:

• 81% to 100% in Asian populations [4][5][6]
• 95.5-96% of Black populations [5][6]
• 46.3 to 70.1% of Hispanic populations [5][6]
• 9.6% of White populations [5][6]

Pathophysiology

In normal fetal development, melanocytes (derived from neural crest cells) are present in the dermis of the embryo by ten weeks gestational age and migrate to the epidermis between weeks 11 to 14 of gestation. No melanocytes should remain in the dermal layer by week 20 of gestation via migration or macrophage clearance. In congenital dermal melanocytosis, melanocytes remain in the dermis and actively produce melanin. The blue-gray color of affected skin can be explained by the Tyndall effect, where dermal melanin scatters the shorter wavelengths of light (blue light), which reflect to the skin surface. An extracellular fibrous sheath protects the dermal melanocytes. However, this sheath becomes gradually lost and destroyed during fetal life and early childhood.[1]

Histopathology

 Spindle-shaped cells that contain pigment located between collagen fibers deep within the dermis.

History and Physical

Congenital dermal melanocytosis commonly appears as a single or multiple hyperpigmented macular lesion(s) on the lower lumbar, sacral, or gluteal surface. The pigmentation of the lesion ranges from dark grey, blue, to blue-green. The shape of the lesion can vary from round, oval, or irregular. These lesions can appear at birth or shortly after birth.[1] A majority of cases have less than 5% total body surface area involvement. Aberrant lesions are classified as extra-sacral, and they can occur on the lower extremities, upper extremities, groin, shoulder, and chest.[2] However, extra-sacral lesions that involve the face or orbits may be Nevus of Ota.

Congenital dermal melanocytosis lesions commonly fade by 1 year old, rarely persisting after 6 years old.[3][4] Lesions that are extra-sacral in location, greater than 10 cm, or are darker in color are the cases more likely to persist after 1-year-old.[2]

Asking parents or caretakers about the onset of lesions and the location of the affected site will aid the clinician toward the correct diagnosis. Clinicians should perform a detailed history and physical and use their clinical judgment to assure that congenital dermal melanocytosis is not confused for other possible diagnoses. Congenital dermal melanocytosis can resemble the bruises that occur in non-accidental trauma. Documentation of these lesions on initial evaluation is important to help delineate from suspected abuse in subsequent visits. Congenital dermal melanocytosis should also be differentiated from other dermal melanocytoses such as nevus of Ota (melanocytic pigment around the face and orbits, usually in a unilateral trigeminal nerve distribution) or nevus of Ito (melanocytic pigment involving the neck, supraclavicular and scapular regions).[2]

Evaluation

Congenital dermal melanocytosis is a benign condition, and further laboratory, radiographic, or histologic workup is not necessary.[1]

Ophthalmological evaluation is required in the case of Nevus of Ota (oculodermal melanocytosis), especially if involvement of the sclera is seen.

Treatment / Management

Congenital dermal melanocytosis will commonly fade within 1 year, rarely persisting after 6 years old. However, for extra-sacral lesions can be treated for cosmetic purposes. A previous case of congenital dermal melanocytosis involving the mandibular area reported significant improvement after four treatments with a 755-nm Q-switched alexandrite laser.[7](B3)

Differential Diagnosis

Differential diagnosis of gray-blue lesions includes other dermal melanocytoses and non-accidental trauma. Nevus of Ota (oculodermal melanocytosis) will typically involve the face & orbits in a unilateral trigeminal nerve distribution. Nevus of Ota does not regress and can be associated with orbital melanocytoma, which requires resection.[2] Another dermal melanocytosis that does not regress is Nevus of Ito, where the melanocytic pigment involves the neck, supraclavicular & scapular regions. There have been rare cases of malignant transformations noted, particularly if there are fast-growing nodules.[8] Non-accidental trauma should be particularly considered if there are lesions in atypical areas, tenderness to palpation of the lesion, or multiple lesions in various stages of healing.[9]

Prognosis

Congenital dermal melanocytosis is a benign condition that rarely persists beyond the first decade of life. Congenital dermal melanocytosis does not have malignant transformations, unlike nevus of Ota or nevus of Ito.[1]

Complications

For patients with persistent extra-sacral lesions, treatment may be pursued for cosmetic purposes.