Review paper Laser Skin Resurfacing

Transcription

1 Review paper Laser Skin Resurfacing L. Bijnens, E. Oost Submitted for publication Telephone: (+27 71) Abstract Cosmetic surgery has substantially gained in popularity over the past years, and advanced technology, like ablative skin resurfacing using lasers, has been one of the primary drivers [39]. The technology has been available since the mid 1990 s, but the prolonged and involved recovery associated with it, initially limited its application and general acceptance by an informed public [39]. More recently, this lead to the introduction of non-ablative technologies and intense pulsed light for skin rejuvenation. However, so far none of the non-ablative dermal remodeling modalities have been able to deliver results anywhere near full surface ablative resurfacing for treatment of photodamage, rhytids, and textural disturbance of moderate or greater severity [37],[11]. Another approach is to careful optimize the parameters of ablative lasers, such that the immediate dramatic results that the general public demands can still be obtained, but with greatly reduced patient downtime and discomfort during treatment. In this review article, the advantages, shortcomings, as well as applications of the different laser resurfacing technologies shall be discussed. I. INTRODUCTION Skin aging, presenting with rhytides and photodamage, and scarring from severe acne, surgery, or trauma are cosmetic disfigurements which may cause psychologic trauma and prompt patients to seek advice about treatment. Photo-damage accounts for more than 90% of the unwanted changes in skin appearance. Solar damage of the skin leads to epidermal abnormalities, such as lentigines and actinic keratoses, and the degeneration of collagen, which results in the formation of rhytides and telangiectasias [34]. Clinically, these changes include fine to coarse wrinkling, laxity, leathery and coarse skin textures progressing to irregular pigmentation, dry scaling and roughness of the skin surface along with telangiectasias and skin sallowness. Histologically, solar elastosis results in the deposition of an abnormal, yellow elastotic material in the upper dermis that replaces normal collagen and elastin and does not have the resiliency of normal elastic tissue [29],[28],[13]. Ultraviolet alterations present as a thickened, basket-woven stratum corneum; a thinner or atrophic epidermis; generalized epidermal cellular atypia; irregular melanin dispersion; and abnormal-appearing elastic fibers in the dermis [28],[50]. Before the advent of laser resurfacing, both chemical peeling and dermabrasion have been used for resurfacing damaged skin. Dermabrasion as well as chemical peeling have been well known to exhibit the potential for the formation of keloids and hypertrophic scars, and can result in permanent hypopigmentation. In addition, dermabrasion exhibits poor depth control, while chemical peels are cardiotoxic, nephrotoxic and hepatotoxic [34]. Resurfacing with lasers is currently recognized as the most effective and safest modality for the treatment of rhytides and photo-damaged skin [37]. Ablative technologies that produce superficial vaporization remain the gold standard among lasers for treatment of photodamage, rhytids, and textural disturbance of moderate or greater severity [37]. Nevertheless, in spite of the efficacy of the early lasers for resurfacing, the demand for ablative laser skin resurfacing experienced a drop, largely due to the unwillingness of an informed public to undergo the prolonged and involved recovery associated with CO 2 resurfacing [39]. This sparked intensive research to find less invasive modalities for skin rejuvenation which resulted in the introduction of non-ablative technologies and intense pulsed light for skin rejuvenation. Another approach to overcome the problems with the early resurfacing lasers is to stay with ablative resurfacing, but minimize the side effects by choosing the laser parameters in a careful manner. The latter approach lead to the development of the Er:YAG laser. The different laser technologies currently employed for resurfacing will be reviewed and discussed from a historical as well as technical and clinical perspective. Their differences as well as their respective strong points and shortcomings will be pointed out, and the importance of using the appropriate protocol with respect to the resulting efficacy, recovery time, as well as patient comfort are highlighted. II. ABLATIVE VS. NON-ABLATIVE TECHNOLOGIES Laser technologies for non-ablative dermal remodeling have multiplied in response to the demand for less traumatic treatments. Fractional non-ablative treatments have been useful in treating conditions such as mild to moderate rhytides, photodamaged skin, acne scarring, leucodermic scars, melasma, and non-facial skin rejuvenation [11]. However, multiple treatments are required and, compared with ablative lasers, the results are far less dramatic, as the clinical efficacy profile does not match that of the full ablative process, especially with

2 respect to moderate to severe rhytides [11]. Direct comparison studies that compare efficacy between ablative and nonablative modalities still have to be reported and it is a general consensus that, in the absence of such studies, ablative technologies that produce superficial vaporization remain the gold standard among lasers for treatment of photodamage, rhytids, and textural disturbance of moderate or greater severity [37]. The remainder of this article will therefore focus only on true ablative technologies. III. LASER RESURFACING PRINCIPLES The underlying physical principle of laser skin resurfacing is the induction of controlled tissue damage, brought about by heat generated as a result of the absorption of photons by specific molecules present in the tissue. The local reaction and physiological changes of the tissue are highly dependent on both the total thermal load, as well as the particular transient temperature profile the tissue has been exposed to. As such, at lower energies, dermal tissue is coagulated, while with increasing thermal load the tissue molecules will disintegrate with more or less char formation. When exposed to a still higher energy, the tissue evaporates. The objective of ablative resurfacing is to remove the epidermis, as well as those parts of the dermis exhibiting signs of damage, and allow the natural healing processes to regenerate the removed tissue. From the literature review that follows it will become evident that both recovery time as well as the incidence of adverse effects like scarring and hypo-pigmentation, are minimized if most part of the tissue is subjected only to evaporative stimuli, thus limiting residual charring and other thermal damage in the remaining tissue. Theoretical arguments indeed suggested that using the principles of selective photothermolysis (ie, selective tissue heating by preferential light absorption and heat production in the targeted tissue with appropriate wavelengths and pulse durations)[5], the proper selection of pulse parameters would confine the thermal damage and result in decreased rates of scarring, improved clinical responses, and faster healing times. According to the theory of selective photothermolysis put forth by Anderson and Parrish, 3 criteria must be fulfilled to confine thermal damage to a selected target [5]. First, the target tissue must absorb a given wavelength more avidly than the surrounding tissue. Second, the time the laser is in contact with the tissue (or pulse duration) must be less than the thermal relaxation time, which is defined as the time needed for a tissue to lose 50% of its heat. This is essential to minimize nonspecific lateral thermal damage, which can lead to scarring and pigmentary change [24]. Third, sufficiently high levels of energy must be delivered to the target tissue to cause ablation [24]. A. Introduction IV. THE CARBON DIOXIDE LASER The Carbon Dioxide (CO 2 ) laser was one of the first types of lasers in dermatologic surgery and has been used extensively over the past 35 years, because of its ability to efficiently vaporize and cut tissue [45]. Early continuous-wave CO 2 laser technology, when used for skin resurfacing, was limited by undesirable thermal necrosis and scarring of tissue caused by nonspecific heat diffusion into the deeper dermis as well as perilesional normal skin [45],[8],[6],[16],[41]. A zone of thermal necrosis measuring 0.2 to 1 mm thick resulted from tissue temperatures reaching 120 o C to 200 o C or more during ablation, with subsequent char formation. This accounted for limited clinical response, scarring and extensive healing times. Thereafter, the principles of selective photothermolysis have been applied in modifying the CO 2 laser by implementing pulses of shorter duration and higher peak power. Pulsed CO 2 lasers were developed that delivered high-peak powers to maximize lesional vaporization and short pulse durations to minimize thermal injury of normal surrounding tissue [45],[53],[21],[48],[52], [14],[30]. Investigation revealed that, for the 20 to 30 µm thickness of water-containing tissue that absorbs CO 2 laser light, the appropriate pulse duration is less than 1 millisecond [48]. In addition, sufficient energy must be delivered within that short time to achieve tissue vaporization with a single pulse or scan. By delivering sufficient energy to vaporize skin, not only is the lesion removed, but the ablated tissue removes most of the energy deposited, thereby reducing the amount of residual energy for thermal conduction. In this way, only a narrow zone of thermal damage is created. The energy fluence per pulse necessary to vaporize tissue with the CO 2 laser is approximately 5 J/cm 2 [47],[18],[19]. If the fluence is below the vaporization threshold of tissue, the laser coagulates rather than vaporizes the tissue, with resultant thermal damage. The tissues coagulate as heat accumulates from the additive effects of multiple laser pulses or a continuous beam. Char is produced from the carbonization of tissue and enhances further heat conduction and consequent tissue thermal damage. Continued lasing results in crater temperatures exceeding 600 o C creating extensive zones of peripheral damage measuring 1 to 5 mm which simulate burns from electrocautery [36]. Technologically, initial modifications of the continuous wave laser system involved the electronic modulation of the continuous beam of light to produce 0.1 to 1 second duration pulses of consistent power. Next, superpulsed systems were developed that could attain peak powers 2 to 10 times higher and pulse durations 10 to 100 times shorter than previous models. High peak-power single pulses could not be produced because of the fact that these lasers were radio frequency excited. Instead, a train of short-duration pulses at rapid repetition rates (200 to 1,000 pulses per second) were used to generate average powers comparable to continuous wave lasers. Unfortunately, these superpulsed lasers, though showing limited tissue thermal necrosis in animal models, did still not demonstrate the marked clinical improvement without scarring or pigmentary alteration expected in humans [45],[42],[15]. It is suggested that the wavelength of the light produced by the CO 2 laser, 10500nm, which corresponds with an absorption coefficient of about 1000cm 1, imposes

3 a fundamental limit to the amount of residual thermal damage that can be achieved by manipulating the remaining system parameters. This becomes plausible when one observes that an absorption coefficient of 1000cm 1 results in a near-gaussian distribution of captured photons, extending about 20 to 30 µm in the tissue at the end of every pulse [48]. This necessarily results in a considerable volume of damaged tissue - and heat - left behind in after the proximal part of the tissue is evaporated. B. Side effects and complications There is no doubt that CO 2 laser resurfacing is capable of achieving good correction of wrinkles and solar damage. However, short-term and long-term side effects are associated with CO 2 laser resurfacing. Expected reactions include temporary skin fragility, peeling, and redness, lasting from 1 to 3 months. Common short-term side effects include milia and acneiform eruptions, seen in up to 84% by Bernstein et al. [9]. Preoperative topical retinoids may reduce the incidence. Perioperative herpes simplex virus infection can be prevented with prophylactic doses of valacyclovir in a patient with a history of recurrent herpes simplex. Postoperative bacterial and candidal infection are uncommon but associated with prolonged use of occlusive dressings or poor postoperative wound care. Occlusive dressings can be removed at 48 hours postoperatively in the office. Debridement of crust and proteinaceous exudate with cool compresses is then performed to clean the site as thoroughly as possible and assure that re-epithelialization is not delayed because of inadequate wound care [37]. Common delayed side effects include hyperpigmentation and hypopigmentation. The incidence of post-co 2 hyperpigmentation varies with skin type but ranges from 26% to 36% [31],[3],[40],[46]. Hypopigmentation is a delayed complication occurring in 8% to 19% of patients [31],[3],[40],[10],[46]. Hypertrophic scarring can be seen in up to 2% to 3% of patients and responds to intralesional Kenalog alone or in conjunction with pulsed dye laser [9]. The incidence of side effects seems to be comparable with the high-energy pulsed CO 2 laser and the continuous-wave CO 2 laser with a scanner attachment [9], two different technologies presently used to comply with the principles of selective photothermolysis. Hyperpigmentation is more likely in darker skin types. Therefore, most laser surgeons hesitate to resurface patients with type IV or higher skin type [37]. Permanent hypopigmentation may be idiosyncratic or result from overly aggressive resurfacing in severely photodamaged skin. Peripheral feathering at the borders of the treatment site or treating with a gradient of passes that attenuates at the periphery can minimize the color and texture contrast between sun-damaged and resurfaced skin [37]. Postoperative wound care with the CO 2 laser is essential for optimal results. To avoid substantial crusting from serous exudate from the denuded cutaneous surface, hydrogels or bioocclusive membranes are often applied for the first 48 hours [37]. Another practical issue is that of anesthesia. Although topical anesthetic (EMLA or lidocaine ointment under occlusion for 1 to 2 hours preoperatively) can provide some relief, it is usually not sufficient for large cases or those involving more than 2 passes. Nerve block (supraorbital, infraorbital, mental) used in combination with tumescent anesthesia infiltrated in the lateral aspects of the face is usually required for fullface CO 2 laser resurfacing in the absence of IV sedation [37]. Anxiolytics, given 30 minutes before the procedure, can reduce the amount of lidocaine required to maintain comfort. A. Introduction V. THE ERBIUM YAG LASER Most of the problems associated with CO 2 laser resurfacing are caused by nonspecific thermal effects, leading to coagulation necrosis to a variable degree in the dermis. The degree of coagulation necrosis appears to increase exponentially with each laser pass, leading to unpredictable results when attempting to treat deeper wrinkles. Furthermore, this thermal damage leads to intensive and prolonged erythema, with a significant risk of scarring [49]. From previous discussion, it is clear to the reader, that an ideal ablative resurfacing laser should employ a wavelength with the strongest possible absorption of the target chromophore, should feature short pulsewidths (in the microsecond range, as well as high energy output per pulse. This combination of features ensures the highest possible selectivity between the extend of the ablated zone and the coagulated zone. The Erbium:Yttrium-Aluminum-Garnet (Er:YAG) laser features a wavelength of 2940nm. When operated with short pulses (SP-Er:YAG), it provides cleaner ablation, characterized by a thinner zone of thermal damage resulting in considerably less shorter healing time and a lower rate of post-procedure side effects compared with SP CO 2 resurfacing lasers [4],[22]. The intensity and duration of postoperative erythema are considerably less than with CO 2 laser resurfacing, as is the degree of hypopigmentation [49]. The Er:YAG laser produces a different tissue reaction compared with the CO 2 laser because of the greater absorption by the target chromophore, water. Erbium:YAG lasers are flashlamp-pumped crystal lasers that emit light at a wavelength of 2940 nm. The absorbtion coefficient of water at this wavelength is 12500cm 1, which is more than 10 times the value of a CO 2 laser. This means that nearly all of the energy is absorbed in the epidermis and papillary dermis, yielding superficial ablation and less underlying thermal damage compared with the CO 2 laser [4],[32]. In addition, vaporization of water by the Er:YAG laser in the ablated epidermis and superficial dermis allows cooling of the tissue as the heat escapes as steam and decreases the heat transferred to the surrounding tissues. This allows the Er:YAG laser to be used for several passes over the ablated area without greatly increasing the zone of thermal damage [32]. Each pass with a short-pulse Er:YAG laser ( microseconds) ablates approximately 20 to 25µm (at 5 J/cm2) [22]. Depth of thermal damage has been shown to be 30 to 50 µm at fluencies of 5 to 8 J/cm2, compared with 50 to 200 µm with the CO 2 laser at fluencies of 3.5 to 6.5

4 J/cm2. [26]. In addition, it appears that even with the multiple passes of the Er:YAG laser, the depth of underlying thermal damage is limited to 50µm [32],[35]. With multiple passes at 5 J/cm2, it may approach that seen with the pulsed CO 2 laser [4],[22],[38]. No visible contraction of dermal collagen fibers is observed with sub-epidermal passes of the shortpulse Er:YAG during resurfacing at high energy levels per pulse. Collagen contraction occurs at 55C to 60C and relies upon heating of the dermal tissue [4]. However, when this effect is desired using an Er:YAG laser, one can include in the treatment regime a number of pulses at lower energies, at higher pulsewidths, and/or at higher pulse repetition rates. The superficial tissue ablation achieved with the SP Er:YAG laser is most advantageous for treatment of mild to moderate rhytids such as those in the periorbital region because the skin is thin, and excess thermal damage may result in scarring. Rapid re-epithelialization and resolution of erythema after SP Er:YAG resurfacing has been demonstrated by numerous investigators [49]. Clinically, three helpful visual endpoints can guide the operator: petechial bleeding, a chamois color, and visual effacement of rhytids [23]. Petechial bleeding occurs as the ablation enters the papillary dermis. A chamois color is seen as the depth of ablation reaches the mid-papillary dermis [23]. Longer-pulse (i.e. 10 milliseconds) Er:YAG lasers have been shown to increase the zone of underlying thermal damage to approximately 60 µm, which in certain cases may result in greater skin tightening but increased risk of secondary side effects such as erythema and hyper and hypo-pigmentation [38]. B. Facial resurfacing of rhytids and photodamaged skin Initial experience with the SP Er:YAG laser confirmed decreased healing time and less prolonged erythema compared with high-energy CO 2 laser resurfacing. The rapid re-epithelialization and reduced postoperative erythema were confirmed by multiple investigators. Teikemeier and Goldberg [44] reported that patients treated with 1 pass of the SP Er:YAG laser (350 microseconds, 2.5 to 5.0mm spot, mj) re-epithelialized in 4 to 10 days. Erythema resolved in less than 2 weeks. No pigmentary changes or scarring were observed, and all patients experienced clinical improvement of rhytids based on comparison of before and after photos at 3 to 8 weeks [44]. Similar results were reported by Perez et al. [35] in 15 patients treated with SP Er:YAG (4-5 J/cm 2, microseconds, 5-mm spot). The mean healing time was 3.2 days. Erythema dissipated completely within 3 to 6 weeks, and redness faded to pinkness in a mean of 7.1 days. Most wrinkles treated were class II rhytids. Of 15 patients, 8 showed marked improvement (50%-75% of class I-II rhytids improved), and 6 of 15 had moderate improvement (25%-50% of class I-II rhytids improved) [35]. Note that these results were obtained with a single pass. Khatri et al. used a SP Er:YAG laser for full-face resurfacing for facial rejuvenation (300 microseconds, 5-mm spot, 5 or 10 J/cm 2 ) with a single pass [27]. Patients were able to tolerate treatment with pre-application of topical anesthetic alone. On a scale of 1 to 5, the mean improvement in appearance as graded by investigators was 1.8 at 1 week, 2.1 at 1 month, and 1.7 at 3 months with the 5 J/cm 2 fluency, and 1.6, 2.5, and 2.1, respectively, with 10J/cm 2 [27]. Comparison of 2 commercially available SP Er:YAG lasers with different programmable overlap features failed to reveal significant differences in efficacy [7]. Patients underwent fullface 1-pass resurfacing with an additional 2 to 3 passes over the periorbital and perioral areas with topical anesthetic. They found a 58% improvement in pigment irregularities and 54% improvement in texture. Periorbital and perioral areas showed a 43% decrease in appearance of fine wrinkles at 3 months. No difference in long-term outcome with the 2 different lasers was appreciated. Patients were able to return to work a mean of 3 days post-procedure, and erythema resolved in 5 days. No long-term side effects were reported [7]. Before the SP Er:YAG laser, laser resurfacing procedures were limited to facial regions because of an increased risk of scarring and dyspigmentation below the jawline. Goldman et al. [17] reported the use of SP Er:YAG for treatment of photoaging on the neck. Twenty patients were treated with 2 passes using variable methodologies. External observers reported a 39% mean improvement of skin texture and a mean of 37% improvement of skin color at 3 months. Histologic evaluation at 6 weeks showed an increase in new dermal collagen and normalization of the dystrophic epidermis. No permanent adverse events were reported [17]. Lengthening the pulse duration of Er:YAG lasers increases tissue heating below the zone of ablation, which may or may not produce improved clinical efficacy but also increase the potential for adverse effects. Longer-pulse Er:YAG laser resurfacing has demonstrated a slight increase in the intensity of postoperative erythema but similar re-epithelialization times to the SP Er:YAG. In 1 study, 6 patients underwent a split-face treatment at 2 different pulse durations using an LP Er:YAG (1 pass, 0.5 and 4.0 milliseconds, 7.0 J/cm 2 )[33]. Mean time to re-epithelialization was 3.6 days, and most patients were comfortable returning to work at 4 days. No significant difference in healing/re-epithelialization or erythema at postoperative day 7 was appreciated between the 2 different pulse durations. There was, however, increased erythema at postoperative days 3 to 4 on the side treated with the 4.0-millisecond pulse duration. In another study, Patients who underwent serial 1-pass laser peels demonstrated increased elastin fibers and accentuation of the horizontal bands of collagen in the papillary dermis. Serial resurfacing was well tolerated and may be an attractive option for patients looking for more improvement with limited downtime [33]. Although initially, the Er:YAG laser was thought to only be useful for the eradication of mild to moderate-depth rhytids, it is now an established fact that much of the literature regarding the limited utility of the Er:YAG laser for superficial rhytids only was based on the use of lower fluencies(up to 10 J/cm 2 ). With devices that are currently available, fluencies as high as 240 J/cm 2 ) can now be used with multiple passes, allowing the

5 treatment of deep rhytids and acne scars with equal or better results than CO 2 systems [32]. Many authors believe that it equals the CO 2 laser in efficacy and has a favorable side effect profile due to improved control of the total depth of injury and decreased underlying thermal injury [12]. Those who note the superior efficacy of the Er:YAG contend that depth of ablation is what determines the degree of dermal remodeling, not the depth of underlying thermal injury [32],[26],[12]. Indeed, as yet there is no evidence that the elastotic tissue, that lies at the basis of the formation of most rhytids, succesfully re-models with the application of heat. Results of the long-pulse (LP) Er:YAG seem to resemble closer those seen with the CO 2 laser. Adrian et al. compared the results of LP Er:YAG laser (10 milliseconds, 5-mm spot, 5 J/cm2, passes) and a high energy pulsed CO 2 laser (300 mj, CPG density 5, 3 passes) for treatment of periorbital rhytids [38]. Similar results were obtained with each laser as judged by the patient and medical personnel. The lead investigator noted that the LP Er:YAG (10 milliseconds) demonstrated increased hemostasis and increased tissue contraction as compared with the SP Er:YAG laser (350 microseconds)when identical fluence was used. Variablepulse Er:YAG lasers allow the operator to achieve superficial ablation with or without deeper thermal injury by adjusting the pulse width [38]. To reap the perceived benefits of thermal injury and still achieve faster healing, some laser surgeons have used a sequential approach, treating first with short pulsewidths followed by a long pulsewidth-pass. C. Other indications Facial resurfacing of rhytids and photodamaged skin are of course not the only applications for which the Er:YAG laser is safe and effective. Kahtri reported extensively on the use an Er:YAG laser for the ablation of cutaneous lesions [25]. Other research that has been published includes revision of postburn scars [2], treatment of melanin-induced benign dermal lesions [20], treatment of Balanoposthitis chronica circumscripta benigna plasmacellularis Zoon [51] and treatment of diffuse plane xanthoma of the face with the Erbium:YAG laser [43], among others. Afzal et al. demonstrated the superiority of the Er:YAG for laser resurfacing of patients with skin type IV [1]. VI. CONCLUSION While non of the non-ablative, neither the ablative fractional technologies, developed to overcome the extended recovery time and occurrence of complications with CO 2 resurfacing, have been showing to deliver the same clinical results as CO 2 laser full ablation, it has been shown that the Er:YAG laser can be used for both mild cases of resurfacing as well as for treatment of class III rhytides with the same efficacy as the CO 2 laser, but with a recovery time and complication incidence profile comparable to non-ablative techniques. 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