Hyperpigmentation is the darkening or increase in the natural color of the skin, most often due to hypermelanosis, which is an increased deposition of melanin in the epidermis or dermis.
This can be associated with a multitude of clinical conditions, ranging from normal variations of skin color to acquired and inherited syndromes.
Diagnosis of hyperpigmentation includes physical examination and a detailed history.
A complete skin examination should be performed under visible light to observe important clinical parameters, including the extent of the pigmentary abnormality, distribution, pattern, color hue and morphology of individual lesions.
Under natural light, epidermal hypermelanosis appears light brown to dark brown in color, while dermal hypermelanosis has a bluish or ashen gray hue with margins less defined than epidermal hypermelanosis.
Complete skin examination should include observing these general features with the naked eye, and then further examine them through dermoscopy.
Next, hyperpigmented skin lesions may be examined under a Wood's lamp, which emits low wave ultraviolet.
A light that allows a better visualization of variations in skin pigmentation.
This is done in a darkened room with the Wood's lamp held at 4 to 5 inches from the skin, to observe any subsequent fluorescence.
Under a Wood's lamp, epidermal hypermelanosis shows enhanced pigmentation, while dermal hypermelanosis doesn’t.
Finally, a skin biopsy for histopathologic evaluation is not routinely performed for the diagnosis of all hyperpigmented lesions, but it may be necessary when the clinical diagnosis is uncertain or suggests malignancy.
The most frequent benign hyperpigmented skin lesions are melanocytic nevi, most commonly known as moles.
These are benign proliferations of a type of melanocyte called nevus cells, which cluster as nests within the lower epidermis and dermis.
Melanocytic nevi must be differentiated from malignant melanoma using the mnemonic ABCDE to spot any worrisome signs, where lesions are asymmetrically shaped, borders are irregular or notched, coloration varies within the same lesion, the diameter is larger than 6 millimeters, and the lesion rapidly evolves over time, quickly increasing in size, and can cause skin elevation.
Mind that, although a changing nevus may raise concern for melanoma in an adult, enlargement and increased elevation occur as part of the normal growth of melanocytic nevi in children and adolescents.
Melanocytic nevi can be classified as congenital or acquired.
Congenital melanocytic nevi are typically present at birth or may appear within the first few months of life.
They’re usually small or medium sized, solitary, and may occur in any cutaneous location.
The color can range from tan to black, and the borders are often irregular.
On the other hand, acquired melanocytic nevi appear throughout life due to predisposing factors like familial tendency to have a large number of moles, degree of sun exposure during childhood, and skin type, with higher nevus counts seen in individuals with lightly pigmented skin.
Acquired nevi can be further classified as common or banal, and atypical.
Common or banal nevi can have a wide variety of clinical appearances, but they tend to be smaller than 6 millimeters in diameter and symmetric with a homogeneous surface, even pigmentation, round or oval shape, regular outline, and sharply demarcated border.
On the other hand, atypical nevi tend to share some of the clinical features of melanoma, such as diameter larger than 6 millimeters asymmetry, color variability, and border irregularities. Evaluation of melanocytic nevi starts by observing these general features with the naked eye, and then further examine them through dermoscopy.
The main dermoscopic features seen in both congenital and acquired melanocytic nevi are pigment network, aggregated globules, and diffuse homogeneous brown pigmentation. Now, not only is it important to evaluate the morphology of the nevus in question, but also comparing it to that of surrounding nevi.
In individuals with multiple nevi, the predominant group of nevi that share similar clinical and dermoscopic features defines the "signature nevus", while nevi that appear different from the signature nevi, called "ugly ducklings" or "outliers", and these nevi should prompt suspicion for malignancy.
For definitive diagnosis of suspicious nevi, as well as for treatment, a complete full thickness excisional biopsy may be performed, taking a 1 to 2 millimeter margin of normal appearing skin and part of the subcutaneous fat.
But most melanocytic nevi remain benign throughout the lifetime of a person and require no treatment other than observation.
However, individuals that have a large number of melanocytic nevi should be followed with periodic total body skin examinations at least once a year.
Use of baseline total body photography for comparison on each follow up examination may help the detection of new nevi or changes in preexisting ones.
Finally, individuals should be counseled regarding sun protection.
Now, there are several additional variants of acquired melanocytic nevi, including halo nevi, blue nevi, and Spitz nevi. Halo nevi, also called Sutton's nevi or leukoderma acquisitum centrifugum, are benign melanocytic nevi surrounded by an area of depigmentation that resembles a halo.
This pigment loss is thought to be a T cell-mediated immune response to the melanocytes of that nevus, and often precedes the spontaneous regression of the central nevus.
Halo nevus belongs to the group of melanoma simulators, which are benign skin lesions that may resemble melanoma and require careful evaluation for differential diagnosis.
Upon dermoscopy, halo nevi exhibit the characteristic dermoscopic features of benign melanocytic nevi, represented by globular or homogeneous patterns.
A biopsy is not indicated if the central nevus is banal in appearance.
On the other hand, if there are atypical or worrisome features, then an excisional biopsy of the central nevus can be performed to exclude the possibility of melanoma.
After diagnosis, halo nevi should be monitored on a regular basis to watch out for any changes in appearance or the onset of associated symptoms like pain or itching.
Other than that, halo nevi are asymptomatic and only of cosmetic significance, so no treatment is required.
Blue nevi are benign proliferations of dendritic dermal melanocytes that actively produce melanin.
The blue color is due to the preferential scattering of shorter wavelengths of light by the dermal melanin.
There are two types of blue nevi, common and cellular.
The common blue nevus typically presents as a solitary, uniformly blue to black, dome shaped papule smaller than 1 centimeter in diameter with preserved skin markings.
These nevi often arise in adolescence, and are most often found on the dorsal surface of the hands and feet.
On the other hand, the cellular blue nevus tends to be a larger and more elevated nodule or plaque, measuring at least 1 centimeter in diameter, with a smooth or slightly irregular surface.
Cellular blue nevi may be congenital or acquired, and are most often located on the scalp, face, buttocks, or sacrum.
Small and stable blue nevi require no treatment, while lesions appearing suddenly or undergoing clinical change should get excisional biopsy.
Spitz nevi, also known as spindle and epithelioid cell nevi, are benign melanocytic lesions that often develop during childhood, and they are most commonly located on the face and lower extremities.
Spitz nevi classically appear as uniformly pink, tan, red or red-brown, dome shaped papules or nodules.
They are usually symmetric, well-circumscribed, and smaller than 1 centimeter in diameter.
The surface may be smooth or verrucous, with a clinical appearance that can lead to misdiagnosis as a pyogenic granuloma or wart.
Darkly pigmented lesions are occasionally seen, typically exhibiting a symmetric "starburst" dermoscopic pattern with peripheral streaks.
Lesions tend to present with a rapid initial growth phase, and then undergo involution over time.
Small, stable, and clinically classic Spitz nevi in a child may be monitored over time, while Spitz nevi with atypical clinical features - such as diameter larger than 1 centimeter, asymmetry, or ulceration - should get excisional biopsy.
Now, there are also other benign hyperpigmented skin lesions other than melanocytic nevi, including lentigo, ephelides, seborrheic keratosis, café au lait macules, Becker nevi, melasma, post inflammatory hyperpigmentation, and acanthosis nigricans.
Lentigo or lentigines in plural are small pigmented spots on the skin with a clearly defined edge, surrounded by normal appearing skin.
In contrast to the "nests" of multi-layer melanocytes found in melanocytic nevi, lentigines have an increased number of melanocytes that is restricted to the cell layer directly above the basement membrane of the epidermis.
There are two major types of lentigo: simple lentigo and solar lentigo.
Simple lentigo, also known as lentigo simplex, is the most common form of lentigo.
Lesions often appear during childhood as sharply circumscribed, round to oval, uniformly brown or brownish-black macules that are usually smaller than 5 millimeters in diameter.
There are typically few lesions, with no predilection for sun-exposed sites.
Some individuals may develop a variant of simple lentigo on mucosal surfaces, in particular the lower lip, which is known as mucosal melanotic macule.
Multiple perioral and oral mucosal melanotic macules characterize congenital disorders, such as Peutz Jeghers syndrome.
On the other hand, as the named suggests, the distribution of solar lentigo is limited to sun-exposed areas, in particular the face, dorsal hands, extensor forearms, and upper trunk.
Thus, they can be prevented through the regular use of sun protection, but it does not lead to regression of existing lesions.
Solar lentigo is most commonly known as liver spots or "old age" spots, because their incidence increases with age.
However, solar lentigines can develop in fair skinned children and young individuals who have had significant sun exposure, especially on the shoulders following severe sunburns, developing multiple tan to dark brown macules of variable sizes and often with irregular borders.
Children with a congenital disease called xeroderma pigmentosum develop numerous solar lentigines at an unusually early age.
Now, diagnosis of lentigines is generally based on the clinical appearance, but lesions that are reported to have changed in color or developed a papular or nodular component should get excisional biopsy to exclude malignancy.
Now, lentigines are benign and only of cosmetic significance, so no treatment is required unless the individual desires removal for cosmetic reasons. In this case they can be removed with surgical excision, or lightened with the use of topical depigmentation agents like hydroquinone cream 4% or triple combination cream with fluocinolone acetonide 0.01%, hydroquinone 4%, and tretinoin 0.05%. An alternative treatment is cryotherapy with liquid nitrogen applied for 5 seconds.
Finally, some individuals are treated with lasers that target melanin like the Q-switched ruby, or intense pulsed light therapy.
Moving on, ephelides or freckles are small, well-demarcated, light brown macules, usually 2 to 4 millimeters in diameter, that develop in areas of sun-exposed skin, most frequently in individuals with red or blond hair and fair skin.
These lesions are due to increased epidermal melanin, while the number of melanocytes is normal.
As such, freckles are different from lentigines and melanocytic nevi, which are caused by accumulation of melanocytes in a small area.
The exposure to UV-B radiation activates melanocytes to increase melanin production, which can induce new freckles and cause already existing freckles to become darker and more visible, and their main difference with other hyperpigmented benign lesions is that they may fade with reduction of sun exposure.
Clinically, freckles are a pretty obvious diagnosis, so no further examination is needed.
Now, sunscreen helps prevent new freckles, but it won't get rid of existing ones.
Ephelides are benign lesions and have no propensity for malignant transformation.
For individuals who don’t like their freckles for cosmetic reasons, there are some treatment options that can help lighten lesions to a minimal extent, including topical depigmentation agents, cryotherapy, chemical peels, or laser treatment.
Seborrheic keratoses are very common benign epidermal tumors made up of immature keratinocytes.
They are most common on certain parts of the body like the trunk, arms, and face, and are seen more often as people age.
