What Is a Melanocytic Nevus?
Melanocytic nevus is a benign tumor that is not cancerous and is composed of melanocytes. Melanocytes are melanin-producing cells in the bottom layer of the skin's epidermis, eye, inner ear, etc. They are involved in skin pigmentation. Acquired melanocytic nevus is not present at birth, and the incidence increases throughout the first three decades of life. However, the incidence peaked during the fourth and fifth decades. Later with each successive decade, the incidence decreased and is rare in people older than 50 years of age. A combination of junctional and dermal nevi are the compound melanocytic nevi.
What Are the Causes of Acquired Melanocytic Nevus?
The etiology of an acquired melanocytic nevus remains unknown. But some evidence has suggested that ultraviolet radiation may trigger the development of acquired melanocytic nevi. The degree of skin pigmentation is inversely related to skin pigmentation. Some studies reveal a high number of melanocytic nevus in children with poor sun tolerance. The exact mechanism of why and how this happens is not well investigated yet.
What Are the Signs and Symptoms of Acquired Melanocytic Nevus?
The benign moles are skin tags, raised moles, or flat moles. They are usually brown, tan, pink, or black (especially in dark-colored skin). They are circular or oval and are generally small. Some moles have dark, coarse hair. They are less than a centimeter and are evenly colored.
How Are Acquired Melanocytic Nevus Classified?
They are classified according to the depth as-
- Junctional Nevus- It is present along the junction of the epidermis and the underlying dermis. Compound Nevus- It is present in both the epidermis and dermis. They are lighter in color than a junctional nevus.
- Intradermal Nevus- It is present within the dermis. Compound and intradermal nevi show elevation corresponding to the surrounding skin.
- According to the Presence at Birth- Congenital- present at birth. Acquired- developed later, anytime after birth.
- According to the Histology- Dysplastic Nevus (Clarke Nevus) - A compound nevus with abnormal (dysplastic) cells. They are more prominent in size than the moles and have irregular borders. Hence they resemble melanoma (cancer). They are more likely to develop into a dangerous type of skin cancer.
- Blue Nevus: It is blue and characteristic pigmented melanocytes are present very deep in the skin. Spitz Nevus: It is a variant of intradermal nevus present in children. Giant pigmented nevus are congenital and are large, pigmented, and occasionally have hair. Nevus of Ito: They are also congenital, flat, brownish, and primarily present in the face or shoulder. Mongolian Spots: They are large, deep, bluish, and present at birth but disappear after puberty. Recurrent Nevus: They are the residual melanocytes left in the surgical wound after an incompletely removed nevus surgery, usually seen after six weeks to 6 months. They cannot be distinguished from melanoma.
How to Differentiate Acquired Melanocytic Nevus From a Melanoma?
A dermatologist evaluation is necessary to evaluate moles fully. They are confused with melanoma, which is a type of skin cancer. The American Academy of Dermatology has suggested a basic reference chart to spot suspicious moles, which includes A-B-C-D. They stand for asymmetry, border, color, and diameter. Sometimes, E, which stands for elevation or evolving, is added. If a mole has a change in its color, size, shape, or changes its border, then it is considered suspicious. Also, if a mole is different from others and begins to crust, bleed, itch or become inflamed, it may indicate a developing melanoma. A recent method correlated common characteristics of a person's skin lesion with any deviation from it as an "ugly duckling." It is not easy to diagnose a fair-skinned individual with light-colored hair with this condition. They have lightly pigmented melanomas, which is not easy to observe. The development of pigmentation in a long-standing unpigmented or lightly pigmented nevus is a cause of concern. Generally, a biopsy is needed in this context.
How to Diagnose Acquired Melanocytic Nevus?
A simple clinical examination looking for asymmetry, irregular borders, color variation, diameter greater than 6 mm, and change over time or elevated lesion should be suspicious. The examination should also include the scalp, the palms, the soles, between the toes, and the genitalia. The plantar surfaces are often missed during inspection. If there is a doubt about a skin lesion, a biopsy should be performed. Simple excisional biopsy is the procedure of choice to remove and diagnose a melanocytic nevus. Then they should be submitted for a microscopic evaluation. It is challenging to come to a confirmatory diagnosis without a microscopic evaluation. A laboratory investigation of the blood does not help diagnose a nevus. The microscopic evaluation of a melanocytic nevus shows normal cellular structural appearance with most cells aligned in the dermal-epidermal junction is where they usually are present. But in the case of melanoma, the cells are dysplastic (abnormal in size and shape). If there is more than one type of cellular architecture, the lesion is called a combined melanocytic nevus.
What Are the Treatment Options Available for Acquired Melanocytic Nevus?
Medical procedures for melanocytic nevus are ineffective and inappropriate as they are difficult for managing benign neoplasms. There are no medications which have a role to play in diagnosis or management of melanocytic nevus. They are surgically removed for cosmetic reasons or because of their potential to change into melanoma. Punch excision is used in small lesions. It is a minimally invasive procedure. Large lesions exceeding 1 cm in diameter cannot be removed by shave technique, and they require complete excision. When the complete excisional specimen is provided to the pathologist, they can make the accurate diagnosis because all available criteria can be applied to the lesion. When the biopsy is obtained partially, the size and appearance of the lesion information that underwent biopsy should be forwarded to the interpreting pathologist or dermatopathologist.
Conclusion
The chances of malignant transformation of a melanocytic nevus into melanoma are controversial. But, 10 % of malignant melanomas have a precursor lesion, of which about 10 % are melanocytic nevi. Some preliminary evidence suggests that exposure to ultraviolet radiation in childhood is correlated with the development of melanocytic nevus in the upcoming years. Hence measures to limit ultraviolet light exposure (using sunscreens) might be helpful.
