Melanocytic Nevus

Melanocytic nevi are caused by benign proliferations of skin cells called melanocytes. These skin cells produce melanin, which is the pigment responsible for the color of the skin. Normally, melanocytes are distributed evenly throughout the basal layer of the epidermis, which is the outermost layer of the skin. With moles, there is an increase in the number of melanocytes that accumulate in a small area, forming a cluster of cells that causes a darker spot on the skin. 

Acquired nevi, on the other hand, typically appear as brown, flat spots that may become raised over time and tend to be smaller than 6 millimeters in diameter (i.e., the size of a pencil eraser). They are usually symmetrical, with even borders, and consist of one single color. Acquired nevi are more common in sun-exposed areas, such as the trunk, arms, and lower legs, but they can appear anywhere on the body.

Some nevi have unique characteristics and are referred to by their names. For example, Sutton nevus is a mole surrounded by a round or oval halo that is lighter in color than the rest of the skin. The Spitz nevus is a pink, red, or brown mole that has a dome shape and is most commonly found in the face and legs. Another example is blue nevus, a characteristic mole that has a blue color due to the location of melanocytes deep within the dermis. 

Melanocytic nevi are diagnosed based on the examination of the skin. Trained clinicians may use a magnifying tool called a dermatoscope to help detect features that are not visible to the naked eye. This can assist in the clinical diagnosis and help distinguish common nevi from atypical nevi, as well as malignant lesions like melanoma. Some dermatologists may also photograph certain nevi to monitor for changes over time if the diagnosis is unclear. 

Individuals who have many moles or who have a family history of melanoma may be recommended to perform self-skin examinations regularly to spot any changes within existing moles or the development of new lesions.  

A good way to check for suspicious nevi is to use the ABCDE rule. ABCDE stands for Asymmetry, Border irregularities, Color heterogeneity, Diameter over 6 millimeters, and Evolution, which refers to changes in size, color, or shape over time. The presence of one or more of these features indicates a higher chance of malignant transformation. For a definitive diagnosis of suspicious nevi, an excisional biopsy may be performed to rule out melanoma.

Most melanocytic nevi remain benign throughout a person’s lifetime and require no treatment other than observation. However, several treatment options can help reduce the appearance of moles or remove them altogether in case of cosmetic concerns.

Common treatments include surgical excision and laser therapy. Surgical removal may include shave excision, which involves “shaving” or removing the mole with a sharp blade. This technique is most effective in moles that affect only the epidermis and has the advantage of leaving minimal or no scarring. For deeper lesions, or in cases where there is a higher risk of malignancy, an excisional biopsy may be needed to remove the whole lesion. On the other hand, lasers work by emitting specific wavelengths of light that are absorbed by melanin. Melanin transforms the energy absorbed from the laser into heat that destroys the pigment in the skin, thereby decreasing the appearance of the mole.