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.