Author(s):
- Laser treatment uses high energy radiation at different wavelengths which can be directed at specific targets.
- Laser treatments should only be undertaken by those with appropriate training.
- It is essential to make sure that patients are carefully selected, are fully informed and have an adequate preoperative assessment.
- A variable level of pain is experienced by patients. Surface, local, or general anaesthesia is used as necessary.
- Different types of laser are used to target different tissues in the skin and therefore careful selection of the correct laser is essential. Lasers can target pigment (melanin, tattoo dyes), blood cells, hair follicles, or surface cells (resurfacing).
- Photodynamic therapy (PDT) involves the photoactivation of a topical chemical. It is commonly used to treat solar keratoses, Bowen's disease, and large superficial basal cell carcinoma.
Laser dermatology is an exciting and expanding field, offering new ways to treat a variety of skin conditions and diseases. The field overlaps concepts of medical dermatology, surgical dermatology, and photobiology and requires a broad understanding of these areas to deliver a highly successful laser practice.
This chapter will look at the interaction of light energy and skin tissue: the properties of the light and its delivery to the tissue need to be matched with the condition being treated. The different types of laser and light devices will be considered, as will the common indications for laser treatment and some more rare conditions that can benefit from laser.
Lasers versus intense pulsed light
Lasers and intense pulsed lights (IPLs) are the main devices that will deliver high energy light pulses to the skin. While there are important differences between the two types of device, the terms are often used interchangeably - for convenience, the term 'laser' is used in this chapter when referring to treatment.
The main difference between the two is that laser devices generate a specific wavelength of light, which is used to target a particular tissue component (e.g. melanin). In contrast, IPLs produce a broad spectrum of light. Most IPLs will have an interchangeable filter, so that only a very narrow range of light wavelength is actually emitted to the skin target. This allows the operator to change the filter depending on what type of lesion they are treating. IPLs tend to have a large handpiece with a window, which is applied directly to the skin surface. The beam is broad and not focused.
Laser devices create a laser beam of a single wavelength, which is a collimated, parallel beam of light energy. This can be focused very specifically on a target, for example on a small haemangioma. Laser beams are created when energy is passed through the laser medium, the electrons are excited, and then release energy to return to their resting state. This release of energy is in the form of the laser light, which can be focused on the skin target. Lasers emitted from one type of laser will have quite different tissue interactions compared to a laser from another type of laser - they have specific properties. For this reason, in clinical practice, lasers are often known by the lasing medium used, which can be a liquid (e.g. dye lasers), a gas (carbon dioxide), or a crystal (neodymium: yttrium aluminium garnet).
The advantages of a laser (over IPL) are that the single wavelength provides specificity in treatment, the collimated light means very precise aiming and they can produce very short pulses of light, currently picoseconds in clinical practice.
Lasers emit a beam of light of a single wavelength, which can be selectively absorbed by a target of a certain colour, causing heating and subsequent lysis. This target is known as a chromophore, from the Greek word for 'bearing colour'. The duration of the laser pulse is also set to be selective for the size of the chromophore. Larger targets such as hair follicles take longer to heat up and are slower to cool than smaller targets such as melanosomes. Lysis of the chromophore leaves a residue of smaller particles which are subsequently phagocytosed by macrophages. This concept of selective photothermolysis underpins laser science. Table 25-1 shows which type of cutaneous disorders may be amenable to treatment with which lasers.
Given the concept selective photothermolysis above, the correct laser, or IPL filter, must be selected for each patient, depending on the type of lesion and also the patient's skin phototype. For example, vascular lesions, which contain blood are amenable to treatment by targeting the oxyhaemoglobin in the blood flowing in the lesion. The wavelengths typically used for this will be in the 500-600 nm range.
However, the selection of laser/IPL is also influence by the patient's skin Fitzpatrick phototype. Darker skin contains more melanin, which can also absorb the laser energy - in this case of a vascular lesion, a short wavelength laser (500-600 nm) would be absorbed by the melanin and maybe even burn a darker skinned patient. Therefore, a longer wavelength laser, such as the Nd:YAG which produces a beam of 1064 nm would be selected, as this can still target oxyhaemoglobin but has a lower melanin absorbance on the skin surface.
As well as selecting the type of laser (wavelength) the laser operator must also select the duration of the beam (milliseconds/nanoseconds/pico seconds) and the fluence of energy to be delivered (joules/watts). Guidance on this is out with the scope of the chapter and requires professional training. Some modern lasers will have standard presets for lesion types, although advanced practitioners would be expected to have a deeper understanding.
Laser treatment should be preceded by a full medical history and dermatological examination.
Laser centres should offer a preoperative consultation by a qualified practitioner who can diagnose and manage skin disease and counsel the patient regarding the most appropriate therapy for their condition. It should always be borne in mind that laser treatment may not represent the optimum management for a patient and that patients are not infrequently referred with the wrong diagnosis. Careful patient selection for laser treatment has been shown to be associated with fewer adverse events, more realistic patient expectations, and higher levels of patient satisfaction. The process of patient selection and preparation and an understanding of the cutaneous biology of the lesions to be treated are as important as the laser treatment itself.
Key concepts that the laser practitioner must assess are:
- What is the dermatological diagnosis?
- Is laser an appropriate choice (time/cost/efficacy)?
- What are the target chromophores?
- What is the patient's skin type?
- What laser(s)/IPL filters are required?
- What are realistic outcomes?
- What steps are needed to minimise complications?
Other preoperative considerations are the use of depigmenting agents such as hydroquinones to help reduce complications of post-inflammatory hyperpigmentation and the use of sunscreen pretreatment to reduce the risk of laser-induced burns of tanned skin, depending on the wavelength used.
Patients should be provided with comprehensive written information relating to the laser treatment of their particular condition before obtaining informed consent. The consent form itself should detail possible complications of treatment (Table 25-2). Scarring may be more likely in certain areas such as the chest, shoulders, and back. It is sensible to perform a small test patch using the desired settings before starting laser treatment or increasing the energy (fluence).
Patients should avoid direct sunlight and use a high factor sun block before laser treatment to minimise the amount of pigment in the skin and reduce the risk of complications.
Patients experience varying amounts of pain during laser treatment, and anaesthesia must be adjusted to the needs of the individual patient and the procedure being undertaken. Some lasers have cooling devices attached, which provide a degree of anaesthesia, and many patients will undergo treatment without additional pain relief. Topical local anaesthetics (EMLA®, Ametop®) may be applied under occlusion before treatment but for procedures such as resurfacing or extensive port wine stains local or regional anaesthesia will be required. General anaesthesia is reserved for treatment of young children and other special cases.
A variety of differing aftercare regimes exist, and one may reasonably ask whether all patients need expensive topical therapies post laser. For non-ablative lasers (which have not caused a surgical wound), patients may prefer a cooling gel such as aloe vera which also has anti-inflammatory properties. Other soothing aftercare products include silicone-based creams, some of which may contain copper, thermal water, or other topical anti-inflammatory ingredients as well as a moisturiser or sunscreen.
When the skin surface is broken, thicker emollients such as white soft paraffin/liquid paraffin blends can form an effective skin barrier. These can be combined with antibacterial washes such as chlorhexidine in a lotion base (rather than a soap base).
Lesions around the mouth have a higher risk of infection, particularly Staphylococcus aureus and herpes simplex reactivation. In resurfacing cases, oral prophylactic antibiotics, and antivirals are prudent.
Sunscreens are often advised post laser treatment although their role is not clear in non-ablative treatments. In ablative treatments, there is shedding of the skin surface which may lead to increased penetration of light through a thinner skin surface. Hence, sun protection is considered important to attenuate post procedure hyperpigmentation. The advice regarding sunscreen for other non-ablative lasering may vary depending on the patient's likely exposure. What may be more important is ensuring that the patient is not tanned prior to the next treatment session, to enhance penetration of the laser and reduce the chance of burning.
The main dangers posed by lasers arise from the energy contained within the beam which can produce a thermal burn or ignite flammable materials. The eyes of the patient, operator, and assistants must be protected using goggles or eye shields specific to the type of laser being used. Other risks come from the high-voltage electricity and operator-dependent errors in technique. Those intending to operate lasers should have prior appropriate training.
Careful patient selection for laser treatment by highly qualified medical practitioners has been shown to be associated with a lower rate and better management of adverse events, more realistic patient expectations and higher levels of patient satisfaction. Preparation and selection of patients and an understanding of skin disease are crucial before selecting a suitable laser, if any. Laser centres should offer a preoperative consultation by a qualified practitioner who can diagnose and manage skin disease and counsel the patient regarding the most appropriate therapy for their condition.
There are numerous conditions which consist of fixed abnormal blood vessels in the skin including port wine stain (Figure 25-1), spider naevus, telangiectasia, and various types of haemangioma. The pulsed dye laser (585-600 nm) or the KTP laser (532 nm) is used to target oxyhaemoglobin within these vessels. The pulse duration is set so that larger vessels are targeted but the smaller normal vasculature of the skin remains intact. Lysis of the abnormal vessels quickly produces a well-demarcated bruise which may be quite prominent and lasts for up to 14 days (Figure 25-2). Repeated treatments, approximately eight weeks apart, will be necessary for most patients, and lesions such as port wine stains that evolve over time may require ongoing therapy.
A wide variety of pigmented lesions affecting the skin are amenable to laser treatment. The appropriate laser for each lesion can be selected by considering the cause and location of the abnormal pigmentation. It is important to make a specific diagnosis of pigmented lesions, rather than simply treating 'pigmentation' itself, as the responses and adverse effects vary considerably.
The commonest pigmented lesions are the result of an abnormal accumulation of melanin within the skin. The melanin is contained within melanosomes which are around 0.4 mm in size. A laser with a very short pulse duration such as the 532-nm Q-switched Nd-YAG or Q-switched ruby lasers will selectively target melanin within the epidermis. Solar lentigos, café au lait macules (Figure 25-3) and ephilides (freckles) can all be treated relatively easily in this manner. Between one and three treatments are usually required to achieve patient satisfaction. Lesions that repigment over time can be retreated when necessary.
When the melanin is located in the dermis the greater penetration afforded by a longer wavelength light is required to reach the chromophore. A 1064-nm Q-switched Nd-YAG laser is usually employed in the treatment of congenital naevus of Ota, naevus of Ito and Mongolian blue spots.
Naevi (moles) are the result of a proliferation of melanocytes and often cause cosmetic problems. Their pigment may well be amenable to laser treatment, but this remains controversial as they have a potential for malignant transformation. This potential can range from being extremely small (e.g. junctional naevi) to an appreciable risk requiring regular dermatological review (e.g. giant congenital melanocytic naevi). The effect of laser treatment on the potential for malignant transformation is unknown. Many would suggest that it is negligible but would still be concerned that litigation might arise from any future malignancies in or around the treated lesion.
A second problem is that these malignancies will usually declare themselves through a local pigmentary change which may be masked by a laser that destroys pigment.
Certain types of melanocytic pigmentation are not amenable to laser treatment. Laser treatment of generalised pigmentary disorders such as that associated with Addison's disease should not be attempted, even in exposed sites, as the lack of uniformity of colour after treatment will lead to dissatisfaction. Melasma (chloasma) is the result of an overproduction of melanin in sun-exposed skin. The response to laser treatment is poor and may worsen the condition. Post-inflammatory hyperpigmentation is the result of a temporary overproduction of melanin by melanocytes following inflammation. Laser treatment is likely to cause further inflammation and exacerbate the problem.
Various forms of abnormal pigmentation exist in the skin, which are due to substances other than melanin. Certain drugs cause localised pigmentation of the skin which may be amenable to laser treatment. Amiodarone and minocycline produce pigmentation which may be selectively targeted by the Q-switched Nd-YAG, Ruby, and Alexandrite lasers.
Haemosiderin is an iron-containing pigment that is deposited in the skin following extravasation of red blood cells. This is very common on the lower legs but treatment with laser is not indicated.
The art of inserting exogenous pigments into the dermis of the skin for decorative effect has been practiced for thousands of years. The subsequent granulomatous reaction permanently fixes the pigment in the skin, although this fixation often outlasts the desire to retain the tattoo.
If the colour and consequently the absorption spectrum of the tattoo pigment differs sufficiently from the surrounding skin then it may be amenable to laser treatment. The appropriate wavelength is selected based on the colour of the tattoo (Table 25-3).
There is no uniformity in the constituents or the application of tattoo pigment and thus no uniformity in response to treatment. Some tattoos show significant fading after only one treatment whereas others can prove far more resistant. In general, amateur tattoos will fade faster than professional ones which may require 10 or more treatments. Care should be taken in the selection of treatable tattoos and the patient must be given a realistic assessment of what is achievable for their tattoo. Responsible laser operators may deem some large multicoloured tattoos untreatable from the outset.
Laser treatment of tattoos creates microscopic steam bubbles in the skin, sometimes referred to as laser snow (Figure 25-4), which disappears in a matter of minutes. Initially, there will be no apparent difference in colour but over the next few months macrophages will phagocytose the newly exposed pigment particles and the tattoo will gradually fade. Treatment is therefore carried out on a 2- to 3-monthly basis.
Recently, pico-second wavelength lasers have been introduced to treat tattoos. These have a much shorter duration of laser pulse and therefore do not generate heat within the skin. This results in lower adverse effects and increased efficacy. The pico-second lasers require fewer sessions to remove pigmentation than the Q-switched lasers.
Laser hair removal is carried out using the Alexandrite, Diode, Ruby, or Nd-YAG lasers, the last being more suitable for darker skin types. IPL can also be used, with an appropriate filter for the patient's skin type. The chromophore is melanin in the hair and thermal energy dissipates to and damages the surrounding follicular cells effecting longer term hair removal. Thus white, grey, blonde, or red hair is unresponsive to treatment, and equal care must be taken where the skin is pigmented. Erythema in the treated area can be expected for up to 48 hours. Around six treatments will be required for a satisfactory response.
The carbon dioxide laser (10 600 nm) and the Erbium-YAG laser (2940 nm) have water as their chromophore. All components of the human body contain water and the action of these lasers on the skin cannot truly be described as selective. Rather, they are a destructive entity used to vapourise tissue. They may be applied as a narrow continuous beam to cut tissue which has the advantage of achieving reasonable haemostasis as one proceeds, enabling convenient excision of unwanted tissue, for example, keloids.
Alternatively, 'resurfacing' of the skin is achieved by photothermolysing the epithelial surface of the skin to a reasonably predictable depth in one or more passes with subsequent healing. This method can improve the appearance of superficial lesions, for example, acne scarring, wrinkles, or epidermal naevi.
A satisfactory result will only be achieved by careful patient selection and scrupulous attention to pre- and post-operative wound care. Considerable training is required to operate these lasers successfully and they should only be operated by those with appropriate expertise.
Fractional laser treatment delivers a series of microscopic laser beams which penetrate into the dermis and are evenly spaced across the treatment area. They do not damage the whole area under treatment, but the resulting columns of ablated tissue encourage the formation of new collagen. It is used to treat scarring, wrinkles, and abnormal pigmentation. Similar columns of epidermal and dermal damage can be induced mechanically by use of a metal roller with small protruding spikes, the so-called 'dermarollers'.
Dermabrasion and chemical peels
Superficial lesions such as wrinkles, scarring, and solar damage can be treated by simple abrasion of the skin surface using a motorised tool in a technique known as dermabrasion. Over the following weeks re-epithelialisation from deeper, healthier epidermis around hair follicles and sebaceous glands brings about healing. Local or general anaesthesia is required and despite intensive pre- and post-operative care the procedure may be complicated by abnormal pigmentation, scarring, or infection. A gentler, but less effective approach is to manually abrade the skin by rubbing it with small crystals (microdermabrasion).
A chemical peel typically uses acid solutions to create an inflammatory reaction on the skin, leading to shedding of the skin and new skin formation. Superficial peels will reach the epidermis only, while medium depth peels will remove the epidermis and reach some of the papillary dermis. Deeper peels can reach the deeper dermis. Typical acids used are glycolic acid, trichloroacetic acid and lactic acid, which may be blended with other cosmeceutical agents. Chemical peeling can be used to treat surface changes such as actinic keratosis, seborrhoeic keratosis, and lentigines. Medium depth peels can be used for deeper improvement of acne scars, wrinkles, xanthelasma, and melasma (with caution). Deeper peels are generally superseded by laser. Peels can leave the skin looking lustrious, with removal of fine lines, deeper wrinkles, stimulation of collagen to tighten the skin and make acne scars shallower. However, good results are dependent on correct patient and peel selection: adverse effects include scarring, long-term redness and post-inflammatory hyper/hypo pigmentation.
Non-laser light sources such as IPL have been advocated as cheaper and less invasive alternatives for the treatment of various skin abnormalities including vascular and pigmentary disorders. They emit light over a range of wavelengths and employ filters to achieve some selectivity. IPL has traditionally been used to treat simple vascular abnormalities such as spider naevi erythema in rosacea and cherry angiomas with relative success. However, they are being increasingly used to treat more complex vascular lesions such as port wine stains. They can be particularly helpful at treating heterogeneous vascular abnormalities where there may be venous and arterial aberrant vessels in the same lesion. IPL, being less chromophore specific, can treat a mixed lesion and can cause thermal heating and subsequent coagulation of deep vessels that may be difficult to target by conventional vascular lasers. There is less blood vessel rupture with IPL when compared to laser treatment and consequently less purpura immediately after IPL. Technology is improving, and IPL is being increasingly used to treat a wider range of skin disorders, but as yet they are considered to be less effective than monochromatic lasers. One of the main advantages of IPL is the ability to treat large areas of skin quickly with relatively little 'downtime' for the patients.
Photodynamic therapy (PDT) in dermatology involves the topical application of a photoactivated toxin such as aminolevulinic acid or methyl aminolevulinate to a lesion followed after three hours by exposure to light, usually in the 630-nm range. The effective penetration at this wavelength is 1-3 mm and PDT is used to treat solar keratoses, Bowen's disease and superficial basal cell carcinoma (Figure 25-5).
Current protocols allow the option of activating the toxin with either a lamp, a wearable light-emitting patch, or ambient daylight. The lamp-based method will require the patient to come to clinic and can be quite painful for the 8.5 minutes of illumination. In contrast, the light-containing patch can be applied by a nurse and the patient allowed to go home, returning the power source device once used. Actinic keratosis, but not basal cell carcinoma or Bowen's disease can be treated with ambient daylight. The patient is treated with a chemical sunscreen which will filter out UV light but allow ambient light to still activate the drug. This method is much less painful than the lamp method and therefore can be used for wide areas on the face and scalp.
PDT has also been advocated for use in acne and anti-ageing although its role among the other treatment options has yet to be defined.
Lasers and light-based therapies operate on a principle of targeting specific tissues via a chromophore. This can be naturally occurring such as melanin, or a chromophore added to the skin such as a tattoo, or a light-absorbing molecule as a target, such as gold or aminolevulenic acid.
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