In the embryo, melanocytes are derived from stem cells in the neural crest that normally migrate to the epidermis, where they are scattered along the basal layer. Melanocytes produce melanin within cytoplasmic packets called melanosomes. These contain greater amounts of melanin in darker skinned individuals. The melanin is distributed to keratinocytes via dendrites when stimulated by exposure to ultraviolet radiation and other factors.
Proliferation of melanocytes may result in congenital or acquired benign melanocytic naevi. These present as persisting macules, papules, plaques and nodules. Melanocytic lesions may be due to]
* * * an increase in melanin within the epidermis without an increase in melanocytes (ephilides)
* * * an increase in melanocytes along the basement membrane of the epidermis (lentigines)
* * * nests of melanocytes at the epidermal/dermal junction and/or within the dermis (moles).
Most melanocytic lesions are pigmented, but dermal naevi often present as skin colored or pink lesions. In general darker skin types have darker moles. Sun exposure leads to a greater number of lesions, but they are not confined to sun exposed sites.
Freckles
Freckles (lentigines) are evenly pigmented brown macules. The freckles arising on the nose and cheeks of young children following sun exposure are due to localised increase in melanin production from normal melanocytes. They fade during the winter months, reappearing in summer. More persistent freckles on the face and hands of adults are due to a proliferation of melanocytes along the basal layer.
The number of lentigines increases with age and can be reduced by careful sun protection.
Providing there is no chance that an individual lesion is a melanoma, the following may be helpful to fade freckles]
* * * Anti-aging creams containing hydroquinone, peeling agents or antioxidants (alpha hydroxy acids, vitamin-C, retinoids, azelaic acid, pentapeptide);
* * * Superficial chemical peels (glycolic acid, Jessner's, salicylic acid);
* * * Lasers or flash lamps that produce a green or red light, which are absorbed by melanin.
Results are variable but sometimes very impressive with minimal risk of scarring.
Resurfacing lasers (carbon dioxide and Erbium]
Moles
Most melanocytic lesions can be ignored, as they are harmless. Sun exposure increases the number and degree of atypicality of moles, a good reason for encouraging sun protection.
Moles may be removed for the following reasons]
* * * Possible malignancy]* * * Nuisance moles: irritated by clothing, comb or razor;
* * * Cosmetic]
Surgical removal may entail]
* * * Shave biopsy
* * * Excision biopsy
The coarse hair that sometimes grows in a mole can be removed by shaving. Plucking may cause inflammation resulting in a painful lump under the mole. The hair can only be removed permanently by electrolysis, laser epilation or excision of the whole mole.
Skin lesions that have been removed surgically should always be sent for pathology. If there is concern that a lesion could be a melanoma, it should be completely excised with 2-3 mm margin. If the lesion is too big for this to be practical or the scar will be unsightly, it is preferable to send the patient to a dermatologist for a specialist opinion. Incisional biopsy should be generous (punch biopsy is best avoided).
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