Prioritize laser/phototherapy endpoints to effectively avoid adverse reactions
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2019-04-29
Prioritize the endpoint of laser/light therapy to effectively avoid adverse reactions
Yin Rui
Author's Affiliation: Department of Dermatology, Southwest Hospital, Army Medical University, Chongqing 400038, China
Author's Introduction: Yin Rui, PhD, Chief Physician, Professor, Doctoral Supervisor. Research direction: Basic and clinical application of laser photodynamic therapy.
The use of skin lasers is booming clinically. With the development of economy and technology, more and more skin treatment/cosmetic photoelectric devices are constantly emerging. If operators are not familiar with the principles and performance of the equipment and cannot reasonably adjust the treatment parameters individually, it is difficult to avoid adverse reactions. Due to different wavelengths and different manufacturers, the effective treatment parameters of laser/light therapy equipment will vary. Only by remembering the endpoint reaction during laser/light therapy and paying attention to the warning signs of critical adverse reactions can we effectively target the target and avoid possible adverse reactions.
Effective Endpoint Reactions During Laser/Light Therapy
1. Benign Pigmented Diseases: Laser or intense pulsed light (IPL) treatment relies on the principle of selective photothermolysis to destroy melanosomes, leading to pigment destruction and absorption, ultimately achieving the therapeutic goal. Short-pulse lasers (nanosecond or picosecond) of 532 nm, 694 nm, and 755 nm Q-switched lasers are often used to treat freckles. The endpoint of treatment is immediate skin whitening, lasting 3-20 min, followed by darkening. When using 532 nm laser treatment, purpura is easily observed due to the proximity of the hemoglobin absorption peak. The endpoint of long-pulse (ms) laser or IPL treatment is a slight darkening of freckles without affecting the surrounding normal tissue. There will be mild redness in the surrounding normal tissue, but it will subside within a few minutes. Histopathologically, this slight darkening endpoint reaction is related to the necrosis of chromocytes in the epidermis.
2. Benign Vascular Diseases: The treatment of vascular diseases with lasers or IPL also relies on the principle of selective photothermolysis. The theoretical basis is that oxygenated and reduced hemoglobin in blood vessels can absorb laser energy of specific wavelengths, including 532 nm potassium titanyl phosphate (KTP), 585 nm/595 nm pulsed dye laser (PDL), 755 nm alexandrite laser, 810 nm diode laser, and 1064 nm Nd:YAG laser, thereby destroying vascular endothelial cells. By using the correct wavelength, laser energy, spot size, and pulse width, vascular lesions can be treated. Lesions that can be treated with lasers or IPL include port-wine stains (PWS) and other microvascular malformations, hemangiomas, telangiectasia, erythematotelangiectatic rosacea, spider nevi, cherry angiomas, warts, erythematous scars, and cutaneous dyschromia. Selecting the correct wavelength, combined with appropriate pulse width and energy, can achieve ideal therapeutic effects.
The endpoint reactions produced after treatment with lasers of different pulse widths are also different. For PWS and other vascular malformations, pulsed dye laser (585 nm/595 nm) is most widely used, and purpura is the endpoint reaction of treatment. KTP and IPL can also be used for the treatment of PWS, and their treatment endpoints depend on the wavelength and pulse width. Under the same wavelength and energy, long pulse width may not produce purpura like short pulse width.
3. Hair Removal: The goal of hair removal treatment is to cause irreversible damage to pigmented hair follicles without damaging the pigmented epidermis. The wavelength for hair removal is 600-1000 nm, and the pulse width ranges from 1-200 ms. Ruby laser (694 nm), alexandrite laser (755 nm), diode laser (810 nm), Nd:YAG laser (1064 nm), and IPL mainly target melanin in hair follicles. Nd:YAG laser is relatively safe for treating dark hair in dark skin, and melanin absorbs 1064 nm less than shorter wavelengths, resulting in relatively less epidermal damage. Skin cooling is necessary, especially for people with dark skin. It should be emphasized that no laser or IPL can treat white hair. The endpoint reaction of laser or IPL hair removal is erythema or edema around the hair follicle within minutes after treatment. This endpoint reaction is an eosinophilic inflammatory response related to hair follicle damage. In patients with dark skin, erythema is sometimes difficult to observe.
4. Lasers Without Clear Endpoint Reactions: Fractional lasers and non-ablative mid-infrared lasers do not have specific treatment endpoint reactions. After fractional laser treatment, white or black punctate scabs will appear. Any immediate reaction of non-ablative mid-infrared and lasers indicates dermal necrosis. When performing non-ablative fractional treatment, it is important to use the correct cooling method and avoid pulse overlap to avoid burns.
Warning Reactions with Predictive Value
Warning endpoint reactions are endpoint reactions that can be seen immediately, or manifestations that indicate tissue damage after laser irradiation. These reactions sometimes represent therapeutic responses, but sometimes have a warning effect. They can be mainly divided into the following categories.
1. Nikolsky's Sign: Necrosis of keratinocytes will cause Nikolsky's sign within 5 min. When the blister is gently pressed from the side with a finger, epidermal and dermal detachment will occur. Nikolsky's sign is mainly due to the loss of adhesion between keratinocytes and the dermis. This phenomenon indicates epidermal necrosis, which may be followed by blisters, erosion, or ulcers, thus increasing the risk of infection, causing pigment changes, or scar formation. Therefore, it is necessary to carefully observe whether Nikolsky's sign occurs during treatment, especially when the patient feels particularly painful during treatment. If the patient has a history of sun exposure or darker skin before treatment, Nikolsky's sign is more likely to occur.
2. Severe Pain with Skin Tissue Changes: During skin treatment using lasers, IPL, or other devices, severe pain often indicates an adverse reaction. High-energy IPL treatment may cause temporary skin whitening, followed by redness, swelling, and even blisters. Deeper penetration treatments such as monopolar radiofrequency or ultrasound can damage fat, resulting in small indentations on the overlying epidermis. Second or third-degree burns from photoelectric therapy will manifest as: severe pain, dense erythema, local edema, blisters, epidermal splashing (or flaking or epidermal adhesion to the handpiece), epidermal loss, or ulcer formation. These iatrogenic injuries may result in erosion and/or ulceration, scabbing, pigmentary changes, secondary infection, and scar formation.
When using lasers/IPL for hair removal, if charred hair adheres to the handpiece's contact surface, it can cause the charred tissue to absorb a significant amount of energy, leading to "postage stamp" burns in subsequent treatments. Cleaning the treatment handpiece before and during treatment can effectively avoid adverse reactions.
When using a dynamic cooling device (DCD), improper settings can cause skin frostbite. A discrepancy between liquid nitrogen spraying and laser emission can lead to arc-shaped or crescent-shaped skin damage. Additionally, if the laser handpiece is not perfectly perpendicular to the skin surface, crescent-shaped skin damage may also occur. A warning endpoint is the appearance of bright white frosting on the skin lasting several seconds; this is entirely avoidable with careful attention during treatment.
3. Skin Contraction: Type I collagen is the most abundant protein in the dermis. When the temperature rises to 70℃, Type I collagen undergoes a helical distortion, causing immediate skin shrinkage. This endpoint reaction clearly indicates dermal thermal damage. For some indications, immediate moderate skin contraction is a very useful therapeutic endpoint (especially for ablative laser resurfacing or the last pass of high-density ablative fractional laser). However, dermal damage is undesirable in any treatment; if this reaction is observed, treatment should be stopped and the situation reassessed. This warning sign can also occur during IPL, radiofrequency (RF), ultrasound, or plasma treatment.
4. Charring: If energy continues to be applied after most of the tissue's water content has been removed, charring may occur. A thin layer of black or dark brown material will adhere to the skin surface. Skin charring indicates excessive thermal damage and may result in permanent scarring.
DOI：10.11786/sypfbxzz.1674-1293.20180301
Journal of Practical Dermatology, 2018,11（3） : 129-132
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