E. L. Tanzi, MD and T. S. Alster, MD
Washington Institute of Dermatologic Laser Surgery, Washington, D.C., USA
ABSTRACT
Over the past decade, refinements in laser technology as well as advances in laser techniques have enabled dermatologic surgeons to define the most appropriate lasers to use for different scar types without the adverse sequelae and recurrence rates noted with older surgical revision techniques and continuous wave laser systems.
Key Words: scars, laser, treatment, surgery
Scar Characteristics
Proper scar classification is important because differences in clinical scar characteristics determine the treatment protocol.1 Scar color, texture, and morphology, as well as previously applied treatments, will affect the laser parameters and number of treatments required for optimal improvement.2,3 See Table 1.
Hypertrophic scars are raised, firm, erythematous scars formed as the result of overzealous collagen synthesis coupled with limited collagen lysis during the remodeling phase of wound healing. The result is the formation of thick, hyalinized collagen bundles consisting of fibroblasts and fibrocytes. Despite the obvious tissue proliferation, hypertrophic scars remain within the confines of the original integument injury and may regress with time.
Keloids are raised, reddish-purple, nodular scars which, upon palpation, are firmer than hypertrophic scars. Keloids exhibit a prolonged, proliferative phase resulting in the appearance of thick hyalinized collagen bundles similar to those produced by hypertrophic scars, but extend beyond the margins of the inciting wound and do not regress over time. Although they can be seen in all skin types, keloids appear most frequently in patients with darker skin tones and are related to an inherited metabolic alteration in collagen.
Atrophic scars are dermal depressions most commonly caused by collagen destruction during the course of an inflammatory skin disease such as cystic acne or varicella. Scarring after inflammatory or cystic acne can manifest as atrophic, saucerized, ice pick, or boxcar scars.4 While ice pick and boxcar scars respond best to dermal filler augmentation or punch excision, atrophic scars usually respond well to laser therapy.
| Scar Type | Clinical Characteristics | Preferred Laser Choice | |
| Hypertrophic | Raised, pink-red, limited to site of original trauma | 585nm PDL | |
| Keloid | Raised, deep red-purple, extend beyond original traumatic border | 585nm PDL | |
| Atrophic | Saucer-like or ice-pick indentations | CO2 (10,600nm) Er:YAG (2940nm) Long-pulsed diode (1450nm) Long-pulsed Nd:YAG (1320nm) | |
Laser Treatment for Hypertrophic Scars and Keloids
Progress in laser technology and refinements in technique have made laser therapy a preferred treatment choice for hypertrophic scars and keloids. Studies published using the 585nm pulsed dye laser (PDL)5-7 have demonstrated striking improvements in scar erythema, pliability, bulk, and dysesthesia with minimal side-effects and treatment discomfort. These observations have been substantiated by skin surface textural analysis, erythema reflectance spectrometery readings, scar height measurements, and pliability scores.
Significant improvement in hypertrophic scars is generally noted within a couple of PDL treatments. (See Figures 1A, 1B) Although thick keloids may require the simultaneous use of intralesional corticosteroid or 5-fluorouracil injections to enhance clinical results, the adjunctive use of intralesional corticosteroids does not significantly enhance the clinical improvement seen after PDL treatment in all but the most symptomatic or proliferative hypertrophic scars.7
 Fig 1A Hypertrophic scars on upper lip before treatment |  Fig 1B Scar improvement seen after PDL treatment |
Adjacent, non-overlapping laser pulses at fluences ranging 6.0-7.5J/cm2 (7mm spot) or 4.5-5.5J/cm2 (10mm spot) should be applied over the entire surface of the scar. Energy densities are decreased by 10% in patients with darker skin phototypes or for scars in delicate locations (e.g., the anterior chest). With PDL irradiation, the patient experiences a snapping sensation similar to that of a rubberband. Post-treatment, a mild sunburn-like sensation is produced for 15-30 minutes that is generally well-tolerated; however, some patients may require application of an ice pack.
The most commonly experienced side-effect of 585nm PDL treatment is post-operative purpura, which can persist for several days. Swelling of treated skin may occur immediately after laser irradiation, but generally subsides within 48 hours. Strict sun precautions should be practiced between treatment sessions in order to avoid stimulating pigment production in the treated areas. Subsequent laser sessions should be postponed until any excess pigment has resolved, so that the presence of epidermal melanin does not compromise the effectiveness of the laser. Topical bleaching agents may be used to hasten pigment resolution. Treatments are typically delivered at 6-8 week intervals; however, longer treatment intervals may be necessary for adequate healing in those patients with darker skin phototypes who develop significant postoperative hyperpigmentation.
Laser Treatment of Atrophic Scars
Ablative Laser Skin Resurfacing
Facial atrophic scars can be safely and effectively resurfaced through the proper use of a high-energy, pulsed or scanned carbon dioxide (CO2) or Erbium-Yttrium-Aluminum-Garnet (Er:YAG) laser.2,3,8-11 These laser systems emit high energy densities within extremely short pulses that effect tissue vaporization with limited thermal conduction to non-targeted surrounding skin. Since each laser pass effects a predictable and reproducible amount of tissue vaporization and residual thermal damage, as much or as little tissue can be removed as required by the type of scar being treated.
Atrophic scar resurfacing with a CO2 laser has effected scar improvements of 50%-80%.8-10 A predictable amount of epidermis and papillary dermis is vaporized by a typical CO2 laser resurfacing procedure, with tissue vaporization depths of 20-60µm and zones of thermal necrosis ranging another 20-50µm. Immediate collagen shrinkage with subsequent collagen remodeling accounts for many of the clinical benefits observed after ablative laser skin resurfacing.
More recently, pulsed Er:YAG lasers have also been used for the treatment of atrophic scars.10,11 The short-pulsed Er:YAG laser was developed as a less aggressive alternative to CO2 laser skin resurfacing. The 2940nm wavelength emitted by the Er:YAG laser corresponds to the peak absorption coefficient of water and is absorbed 12-18 times more efficiently by superficial, water-containing tissue than does the 10,600nm wavelength of the CO2 laser. With a pulse duration of 250µsec, a typical short-pulsed Er:YAG laser ablates 10-20µm of tissue per pass at a fluence of 5J/cm2 and produces a residual zone of thermal injury not exceeding 15µm. The precise tissue ablation and limited residual thermal damage result in a faster postoperative recovery and improved side-effect profile as compared to CO2 laser skin resurfacing.2,10 However, because of the limited zone of thermal injury, short-pulsed Er:YAG laser skin resurfacing is hindered by poor intraoperative hemostasis, limited collagen contraction, and substantially less impressive clinical results than with CO2 laser skin resurfacing.
To overcome the limitations of short-pulsed Er:YAG laser skin resurfacing, “modulated” or “dual-mode” (short- and long-pulsed) Er:YAG systems have been developed that combine ablative and coagulative pulses to produce deeper tissue vaporization, greater contraction of collagen, and improved hemostasis. Studies have demonstrated significant clinical improvement in atrophic scars with these modulated laser systems.2,11
Whether a CO2 or modulated Er:YAG laser system is used to treat atrophic facial scars, the goal of treatment is to soften depressions and stimulate neocollagenesis in order to fill in the residual defects. (Figures 2A,B) For a small number of grouped scars, spot laser resurfacing may be a viable option. For more extensive and diffuse scarring, laser treatment should be performed with a scanning handpiece over the entire cosmetic unit in order to prevent obvious lines of demarcation between treated and untreated sites. With the CO2 laser, a fluence of 300mJ is typically used to effect epidermal ablation with one pass. A dual-mode Er:YAG laser operated at a fluence of 22.5J/cm2 achieves comparable results with a single pass. However, most atrophic scars will require multiple laser passes, regardless of the laser system used. Between each laser pass, the partially desiccated tissue must be completely removed with saline- or water-soaked gauze to prevent excessive thermal necrosis in residual tissue.
 Fig 2A: Atrophic scars before treatment |  Fig 2B: After variable-pulsed Er:YAG laser resurfacing |
Side-effects and complications are potentially numerous after ablative laser scar resurfacing.2,8-11 Expected side-effects in the immediate postoperative recovery period include intense erythema, edema, and serous discharge. The degree of erythema is directly correlated to the number of laser passes delivered, but typically improves spontaneously over time without requiring specific treatment. Other possible complications include infection, acne or milia formation, and dyspigmentation. Although laser skin resurfacing can be performed in darkerskinned patients, postinflammatory hyperpigmentation almost always occurs, typically within 3-4 weeks after treatment. This reaction pattern is temporary and its resolution can be hastened with topical bleaching and peeling agents; however, patients must be warned preoperatively that it may persist for several months. The Er:YAG laser is associated with a less complicated postoperative recovery period and less persistent hyperpigmentation than CO2 laser skin resurfacing, which is of particular importance when treating patients with darker skin phototypes.11 Rare but serious complications after ablative laser skin resurfacing include delayed-onset hypopigmentation, hypertrophic burn scars, disseminated infection, and ectropion.
Nonablative Laser Skin Remodeling
As a consequence of the risks associated with ablative laser skin resurfacing, great interest has been shown for less invasive methods to effectively treat atrophic facial scars. Several nonablative laser devices have demonstrated efficacy in the treatment of atrophic facial scars; however, the most popular and widely used are the 1320nm Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) and 1450nm diode lasers.12,13 Each system combines epidermal surface cooling with deeply penetrating wavelengths that selectively target water-containing tissue, thereby creating a selective thermal injury in the dermis without damage to the epidermis. Protocols for treatment often include three consecutive monthly laser treatment sessions with the greatest clinical improvement noted between 3 and 6 months after the final laser procedure.
Improvement of scars by 40-45% has been observed after either 1320nm Nd:YAG or 1450nm diode laser treatment, with results being substantiated by clinical assessments, patient satisfaction surveys, histologic evaluation, and skin surface texture (profilometry) measurements.12 (Figures 3A,B)
 Fig 3A: Atrophic scars before treatment |  Fig 3B: Six months after third 1450nm diode laser treatment |
Side-effects and complications of nonablative laser treatment of atrophic facial scars are generally mild. Transient post-treatment erythema is observed in almost all patients, resolving within 24 hours. Blistering, crusting, and scarring are rare and although the risk of post-inflammatory hyperpigmentation is substantially reduced with nonablative laser treatment (compared to ablative CO2 or Er:YAG laser skin resurfacing), it is still possible—particularly in patients with darker skin phototypes.12 The post-inflammatory hyperpigmentation observed, however, is typically mild and resolves more quickly than that seen after ablative laser procedures.
Although a series of nonablative laser treatments can effect modest improvement in atrophic facial scars with minimal side-effects, the degree of clinical improvement does not equal that of ablative laser skin resurfacing. Therefore, it is critical to identify those patients best suited for non ablative procedures in order to offer realistic clinical expectations and optimize patient satisfaction.
The newest approach in the treatment of acne and atrophic scarring includes the use of a nonablative radiofrequency device. Unlike a laser, which uses light energy to generate heat in targeted chromophores based on the theory of selective photothermolysis, radiofrequency technology produces an electric current that generates heat through resistance in the dermis and subcutaneous tissue, thus stimulating neocollagenesis and collagen remodeling. Preliminary studies14 demonstrate promise in the treatment of acne and, potentially, acne scarring. Further investigation is warranted to determine the role of this novel device in the treatment of atrophic facial scars.
