Lentigines

In most cases, lentigines are caused by exposure to ultraviolet radiation, such as from sunlight or tanning beds. UV radiation causes skin cells called melanocytes to produce a pigment called melanin. Melanin acts as a natural sunscreen that absorbs and dissipates UV radiation, preventing it from damaging the skin. Over time, damage from UV radiation can cause melanin to deposit in the skin, resulting in solar lentigines.

Signs and symptoms of lentigines include a small, well-demarcated area of skin that is darker than the surrounding skin and is homogeneous in color. The most common type of lentigines is lentigo simplex, which are brown or black spots that are present from birth or early childhood and are not associated with sun damage. While completely benign, lentigo simplex lesions can sometimes be mistaken for lentigo maligna, a precancerous lesion that can evolve into melanoma.

On the other hand, solar lentigines are flat, or slightly raised spots with clearly defined edges that develop in areas of the skin exposed to the sun, including the face, back of the hands, and forearms. Their color varies depending on the individual’s skin tone, ranging from light to dark brown or black. Solar lentigos are similar in appearance to lentigo simplex, but they tend to be larger and have a predisposition for sun-exposed skin areas. Most solar lentigines begin to appear in adult life and are commonly known as age spots or liver spots.

In rare cases, lentigines can be a sign of familial syndromes such as LEOPARD syndrome and Peutz–Jeghers syndrome. LEOPARD syndrome is a genetic condition characterized by multiple lentigines, cardiac and genital defects, growth delays, and deafness. On the other hand, in Peutz-Jeghers syndrome individuals develop polyps throughout the gastrointestinal tract, as well as widespread lentigines in the mouth, lips, genitalia, palms, and soles.

Diagnosis of lentigines is based on their clinical appearance. Trained clinicians may also use a dermatoscope, which is a tool that can magnify skin lesions and emit a special light to help detect features that are not visible to the naked eye. With lentigines, dermatoscopy typically shows a lightly pigmented reticular or net-like pattern across the whole lesion. These characteristics can help distinguish lentigines from other hyperpigmented skin lesions like actinic keratoses, seborrheic keratoses, or melanoma (i.e., a form of skin cancer that affects melanocytes). 

The main warning signs of melanoma can be assessed using 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 malignancy. In suspicious lesions, diagnosis is confirmed with a skin biopsy to rule out malignancy.

Treatment of lentigines is not necessary since they have no risk of becoming malignant. However, for cosmetic reasons, several treatment options can help minimally lighten lesions. Common treatments include pigment lasers which emit 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. Other treatment options include cryotherapy, which involves freezing the lesion with liquid nitrogen, topical retinoids, and lightening peels. Topical retinoids act by increasing turnover of skin cells and reducing the production of melanin, whereas peels help to exfoliate the outermost layer of skin, reducing the appearance of pigmented skin lesions.