Pathology of Dermal Melanocytosis

What Is Dermal Melanocytosis?

Dermal melanocytosis is a benign and uncommon skin pigmentation abnormality. The skin appears hyper-pigmented and appears gray or blue-gray. These lesions may be congenital or seen in the later years of childhood or adulthood. The most commonly seen congenital entities of dermal melanocytosis are the Mongolian spot, nevus of Ota, and nevus of Ito. Lesions that appear after birth are Nevi of Hori and Blue nevus.

Lesions of gray and blue patches characterize acquired dermal melanocytosis. They are benign and rare in occurrence. The lesions are generally present on the face and are known as nevus of Hori and acquired bilateral nevus of Ota-like macules. Lesions appear in the early or late stages of adulthood. The etiology of acquired dermal melanocytosis is unknown.

What Are the Various Clinical Entities of Dermal Melanocytosis?

Dermal melanocytosis lesions are diverse and contain both congenital and acquired lesions. These lesions show similar histopathological features like dendritic and dermal melanocytes. Hence, it is necessary to use the clinical correlation between them. The clinical relationship is established by the location of the lesion, its appearance, and the involvement of skin dermatomes.

• Mongolian Spots - These are congenital lesions and appear as constant blue-gray patches on the sacral and buttock areas. It is mainly seen in Asian races and black infants.

• Nevus of Ota - It is also known as oculodermal melanocytosis and nevus fusco caeruleus ophthalmo maxillaris. It is a congenital lesion and affects the areas supplied by the first and second parts of the trigeminal nerve. The lesions are mottled brown-gray or speckled in appearance. The skin, conjunctiva, sclera, tympanic membrane, and oral and nasal mucosa are the most common sites of involvement area. As a result, glaucoma and one-sided hearing loss are seen in many patients.

• Nevus of Ito - It is also known as fusco-caeruleus and is a congenital lesion of dermal melanocytosis. The characteristics are similar to nevus of Ota, both clinically and histopathologically; however, it involves the skin, which is supplied by posterior supraclavicular and lateral brachial cutaneous nerves.

• Nevus of Hori - It is an acquired dermal melanocytosis. The lesions are blue-brown to slate-gray mottled in appearance. It is more commonly seen in Asian races and females. Unlike other dermal melanocytosis lesions, the eyes and mucosa are not involved.

What Is the Pathophysiology of Congenital Dermal Melanocytosis?

Melanocytes (skin cells producing melanin) are derived from the neural crest cells. At ten weeks of gestational age, during fetal development, the melanocytes are seen at the dermis of the embryo. These melanocytes move to the epidermis at 11 to 14 weeks of gestational age. Ideally, after 20 weeks of gestational age, melanocytes should not be present in the dermis due to macrophagic action. However, in dermal melanocytes, the skin cells get entrapped in the dermis while moving toward the epidermis, producing melanin actively. The skin color changes to blue-gray color in dermal melanocytes due to the scattering of blue light (short wavelength) that reflects on the skin's surface. It is also known as the Tyndall effect.

The migration from the dermis to the epidermis is influenced by exogenous growth factors activated by tyrosine kinase receptors. However, few studies have indicated that heparan sulfate (a polysaccharide that helps in regulation between cell and extracellular matrix) and metabolites such as GM1 bind to tyrosine kinase receptors and cause neurological manifestation and atypical migration of neural crest cells.

What Is the Pathophysiology of Acquired Dermal Melanocytosis?

Many hypotheses explain the pathophysiology of acquired dermal melanocytosis. According to one of the theories, acquired dermal melanocytosis can result from the reactivation of dermal melanocytes that were left behind in the dermis during its migration to the epidermal layer. In addition, factors like UV radiation, chemical exposure, chronic inflammation, and excessive sex hormones, mainly estrogen, can stimulate the activation of dormant melanocytes.

Another theory suggests that the descent of melanocytes from the epidermal layer or the descent of melanocytes from the hair follicles can result in acquired dermal melanocytosis.

Lastly, the theory also suggests that acquired dermal melanocytes can result from inflammation or atrophy of the dermal layer of the skin.

What Are the Clinical Manifestations of Dermal Melanocytes?

• Nevus of Ito - It appears as a blue-gray pigmentation, seen on the shoulder and side of the neck.

• Nevus of Ota - It is a macule with blue-gray pigmentation seen in the areas supplied by the first and second divisions of the trigeminal nerve.

• Mongolian Spot - It is clinically presented as single or multiple macules that are blue-gray to blue-green in appearance. The most common sites are the lower lumbar, sacral, and gluteal regions. The shape is oval and rounded. The lesion may be present at birth and usually fade away. Large lesions tend to fade away at a later stage.

What Is the Histopathology of Dermal Melanocytes?

Heavily pigmented dendritic skin cells that produce melanin and melanophages are present in the dermal layer; however, melanophages are absent in the Mongolian spot.

What Is the Prognosis of Dermal Melanocytosis?

Dermal melanocytosis is a benign condition seen mainly in the first decade of life. After that, it fades and, in some individuals, can sometimes persist throughout life. Mortality and morbidity are not seen in dermal melanocytic.

What Is the Differential Diagnosis of Dermal Melanocytosis?

• For Mongolian Spot - The differential diagnosis is bruising, as seen in child abuse.

• For Nevus of Ota - Cafe-au-lait patch and speckled lentiginous nevus.

What Is the Treatment of Dermal Melanocytosis?

Cosmetic and laser treatments are recommended for treating dermal melanocytosis. Laser treatment results vary for different clinical entities of dermal melanocytosis. Cryotherapy, chemical bleaching, and surgical excision are not recommended as they can lead to scarring without giving desired results.

Conclusion

Dermal melanocytosis is frequently witnessed in children by pediatricians and primary healthcare workers. Though it is a benign condition and resolves with time (generally the first decade of life), healthcare professionals need to identify lesions that are different from dermal melanocytosis as it could indicate child abuse or other pathologies requiring further investigation. In addition, since these are hyperpigmented lesions, doctors must educate the children's parents on the lesion's benign nature and that the lesions need no further evaluation and treatments.