The most common benign pigmented lesions associated with photoaging are ephelides (freckles), solar lentigines (sun spots), and mottled pigmentation. Certain dyschromic conditions are also associated with or exacerbated by exposure to ultraviolet (UV) light such as post-inflammatory hyperpigmentation (PIH), melasma, and poikiloderma of Civatte. This chapter reviews laser* principles as they relate to treatment of benign pigmented lesions and conditions seen in photoaged skin and provides a step-by-step approach to treatment. Chronic exposure to UV light also contributes to the formation of neoplastic pigmented lesions such as melanomas and pigmented basal cell carcinomas. Neoplasias are not indicated for cosmetic laser treatments. When treating pigmented lesions with lasers, they must be verified as benign before treatment.
- Anatomy: Solar lentigines also referred to as liver spots and sun spots, are one of the most common benign pigmented lesions seen in the photoaged skin. These brown macules darken and increase in size and number with chronic sun exposure. They are typically located around the periphery of the face), neck, chest, and other sun-exposed areas of the body. Ephelides (freckles) are similar to lentigines but smaller; they darken in summer and lighten in winter. Photodamaged skin often demonstrates mottled pigmentation, with areas of mixed hypopigmentation and hyperpigmentation. Some patients with photoaging have chronically hyperpigmented skin, referred to as actinic bronzing. Pigmented conditions exacerbated by UV exposure include PIH, melasma, and poikiloderma of Civatte. PIH is visible as brown macules or patches arising at sites of inflammation such as acne and trauma and can be a complication of inflammation associated with laser treatments. PIH occurs most often in patients with dark Fitzpatrick skin types (IV– VI). Melasma presents as hyperpigmented reticular patches and brown macules on the face, typically involving the cheeks, upper lip, forehead, and chin. It is frequently observed following a change in female hormonal status such as during pregnancy (chloasma) and in response to oral contraceptives. Although much less common, melasma can also occur on the neck, chest, and forearms. Poikiloderma of Civatte presents as erythematous and/or brown discoloration on the chest, lateral neck and cheeks. Melanin pigment determines skin and pigmented lesion color. Pigmentary changes in the photoaged skin are due to dysregulation of melanin synthesis and deposition in the skin. Chronic UV exposure results in an increased number of overactive melanocytes and disorganized melanin deposition in the epidermis. Chronic UV exposure results in an increased number of overactive melanocytes and disorganized melanin deposition in the epidermis. This results in regions excess with melanin evident as hyperpigmentation such as freckles and lentigines, and regions with melanin deficiency evident as hypopigmentation. Pigmented lesions can be classified based on the depth of melanin accumulation in the skin as epidermal, dermal, or mixed epidermal and dermal. Solar lentigines and freckles are located in the epidermis while PIH, melasma, and poikiloderma of Civatte can be located in either or both of these levels. Benign pigmented lesions and their cutaneous location are summarized in Table 1. A Wood’s lamp may be used to visually determine the depth of melanin pigment in the skin. When illuminated with a Wood’s lamp epidermal pigmentation appears darker with more contrast against the background skin, while dermal pigmentation has less contrast.
- Laser Principles: Laser treatment of benign pigmented lesions is based on the principle of photothermolysis. There are two main categories of lasers used to treat pigmented lesions, pigment-specific lasers that target the melanin chromophore in pigmented lesions, and skin resurfacing lasers that target the water chromophore in dermal tissue.
- Pigment-specific lasers are most commonly used for the treatment of pigmented lesions. They use melanin as the target chromophore, which preferentially absorbs light between 600 and 1200 nm. Melanin has greater absorption at shorter wavelengths and less absorption at longer wavelengths. Lasers that produce light in this range include KTP (532 nm), ruby (694 nm), alexandrite (755 nm), diode (810 nm), Nd: YAG (1064 nm). Many of these wavelengths are available as Q-switched (QS) lasers that generate very short pulse widths, in the nanosecond and picosecond range. Melanosomes are very small in size (approximately one μm) and respond well to these extremely short pulse widths. QS lasers utilize photoacoustic vibration as well as selective photothermolysis for removal of pigmented lesions. Intense pulsed light (IPL) devices emit a band of wavelengths and those used for the treatment of pigmented lesions encompass the desired wavelengths for melanin absorption. When a lesion such as a lentigo is irradiated with a pigment-specific laser, melanin within the melanosome absorbs energy and is heated and melanosome-containing cells (i.e., melanocytes and keratinocytes) rupture. Melanin is then eliminated through lymphatic drainage, phagocytosis, and exfoliation.
- Skin resurfacing lasers: use water as the target chromophore, which significantly absorbs light above 1200 nm These lasers are used primarily for collagen remodeling effects to treat wrinkles and scars, but can also be used to treat pigmented lesions. When skin is irradiated with a resurfacing laser, water in the dermis absorbs energy and is heated. The epidermal and dermal tissue is removed, and pigmented lesions are removed nonspecifically along with this tissue. Nonablative skin resurfacing lasers (fractional) that treat pigmented lesions include 1410, 1440, 1540, 1550, and 1927 nm. Through a process referred to as fractional photothermolysis, these lasers heat and coagulate a portion of the skin in microscopic columns, called microthermal zones. Melanin in the treated microthermal zones is extruded from the epidermis along with other epidermal and dermal debris, thereby reducing unwanted pigmentation. The depth of penetration of these lasers is affected by their water-absorption capabilities, where wavelengths that are highly absorbed by water penetrate superficially, and shorter wavelengths with lower water absorption penetrate more deeply. For example, 1927 nm has greater water absorption than 1550 nm. Consequently, 1927 nm targets more superficial lesions and is effective for treatment of epidermal pigmented lesions such as lentigines and ephelides, whereas 1550 nm penetrates deeper to the dermis and is more effective for dermal pigmented lesions such as melasma. Ablative skin resurfacing lasers (both fractional and nonfractional) include 2790, 2940, and 10600 nm. Ablative skin resurfacing lasers are primarily used for the treatment of wrinkles and scars, but ablation of epidermal and dermal tissue also removes pigmented lesions.
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