Laser Resurfacing and Remodeling of Hypertrophic Burn Scars
Laser Resurfacing and Remodeling of Hypertrophic Burn Scars
In this prospective, before-after cohort study, we provide long-term data supporting the hypothesis that laser treatments significantly improve the objective and subjective characteristics of hypertrophic burn scars. Using provided-rated and patient-reported instruments, we demonstrated that PDL, CO2, and other lasers rapidly and perhaps permanently lower both VSS and UNC4P, 2 scar assessment tools that measure the thickness, redness, pigmentation, itching, pliability, and pain of hypertrophic burn scars. At more than 2 years of follow-up, VSS had dropped from 10.43 to 3.29, whereas UNC4P had fallen from 5.40 to 1.74. These results were achieved after an average of 5.3 sessions per patients (SD 3.4, median 4), with a complication rate of 4.6% per session and extremely rare adverse events, all related to anesthetic issues. Furthermore, our subgroup analysis revealed that both children and adults benefit from both early and late laser treatments, with the greatest gains occurring in laser sessions that occurred less than 18 months after injury. Decay curve modeling, to account for the natural, incremental improvement of hypertrophic scars, indicates that laser therapies dramatically shift the curve asymptotically toward lower VSS scores. Laser treatments have the potential to accomplish 2 goals: (1) accelerate the time toward maturation of the hypertrophic burn scar, and (2) lower the final endpoint predicted by nonoperative, conventional management.
The precise mechanism accounting for the effect of laser therapy on hypertrophic burn scars has not been elucidated. In fact, applying heat and light to previously damaged skin may seem to be counterintuitive. Indeed, the potential exists to exacerbate the hypertrophic scarring, if burned areas are treated with the wrong laser, the wrong settings, and in the wrong sequence. Nevertheless, several high-quality systematic reviews, consensus reports, and recent clinical trials strongly support the use of laser- and light-based therapies for the treatment of hypertrophic burn scars.
The rationale use of specific lasers, in a defined sequence, to address specific pathological components, allows the provider to manipulate the hypertrophic burn scar and improve specific characteristics such as thickness, redness, and stiffness, which in turn improves the subjective findings of texture, itching and pain, and pliability. Through selective photothermolysis, the 595-nm PDL targets the microcapillaries of hyperemic, immature burn scars, coagulating these vessels and turning off some of the inflammatory component. Once the scar is more mature, the 10,600-nm CO2 laser is next used to target water in abnormal collagen, several millimeters below the surface of the skin. When applied in a fractional pattern, columns of abnormal scar are ablated, allowing new collagen to form in a controlled manner, with rapid reepithelialization of surface. Recent work suggests that in addition to apoptosis of fibroblasts in these microthermal zones, or "MTZs," the hypertrophic scars undergo upregulation of matrix metalloproteinase 1 with alteration of types 1 and 3 procollagen levels and down-regulation of transforming growth factors and basic fibroblast growth factor. Not only are these changes evident in the MTZs, but the entire thickness of the dermis seems to be affected. These molecular and cellular findings are consistent with the clinical observation that fractional CO2 laser treatments, while ablating only the superficial 0.5 to 2.0 mm of the dermis, improve elements that involve the entire thickness of the dermis, such as pliability.
This study provides convincing evidence that the early benefits, which we previously reported, are maintained or further improved at long-term follow-up. Our previous study indicated that the first session yielded the largest drop in VSS and UNC4P, but additional sessions contributed to incremental, statistical reduction in these scar scores. The clinical value of this finding is that although patients may have a dramatic response after 1 to 2 sessions, subsequent treatments may produce specific improvements in components of the hypertrophic burn scars, such as height, stiffness, pruritus, and even pain. For this reason, we recommended several sessions initially, with our overall treatment plan dependent upon the response of the patient to these laser treatments. With the new data from this study, we believe that treatment beyond our original recommendation of 2 to 4 sessions may be warranted, to improve such objective measures as redness, thickness, color, and stiffness. We speculate that not only does laser therapy improve the physical aspects of the hypertrophic burn scar, but that this new approach might eliminate the need for some surgical procedures or decrease the extent of reconstruction that may be indicated.
With this study's follow-up period of 30 months, we addressed a major shortcoming of the prior study: limited follow-up with unknown long-term outcomes. Although laser treatments improved hypertrophic burn scars over a short time horizon, we now know that these therapies yield results that remain stable over 2 years (UNC4P) or continue to improve (VSS). Clearly, laser treatment accelerates scar maturation, clinically, as evidenced by lowering of the decay curve that normally describes the incremental improvement of burn scars, over time. One difference between the long-term follow-up group (30 months) and the short-term cohort (5 months), which must be considered, is that the patients who were tracked over a longer time period had more laser sessions than the group with the shorter follow-up (mean 5.25 vs 2.82 sessions, median 4.0 vs 3.0 sessions). This is not surprising, but these extra sessions must be factored into the interpretation of the final outcomes, apparent at the end of the study period. At the very least, one can conclude that additional sessions effect additional improvement; this was apparent for VSS but not necessarily UNC4P, the latter of which remained stable. In neither case did the objective nor subjective measurements drift back or return to baseline. Scars continued to improve, remained stable, and did not worsen.
Although this project represents the largest, before-after cohort study to date, with long-term follow-up of more than 2 years, this study still has legitimate limitations that will be addressed in future clinical trials. First, not all patients treated in 2011 were available for follow-up in 2013, limiting the sample size of our final cohort. Nevertheless, we were able to demonstrate statistical improvement in hypertrophic burn scars in the smaller cohort, at 30 months of follow-up. Second, both VSS and UNC4P do not provide enough detail to personalize treatments, based on which scars might benefit from certain lasers. In the future, clinical trials will need to include more objective metrics, such as scar thickness documented by ultrasound, degree of rubor determined by a chromometer, and elasticity measured by a curtometer. Furthermore, both burn-specific and nonburn instruments, such as the BSHS-B and SF-36 or SF-12, will be necessary to more accurately determine quality of life. Third, even though the evaluators were blinded to previous scar scores and treatment parameters, the evaluators still carried a bias in favor of the success of this project, potentially influencing the grading of the scars by both provider and patient. Fourth, this before-after cohort study did not include a control group that received only medical therapy, thereby preventing the investigators from determining the observed, natural history of these scars, which tend to improve over time. Fifth, the order of using different laser therapies was not examined and may have a profound impact on final outcomes. To address these issues, the authors recognize that a blinded, randomized, multiple-arm, controlled trial will be necessary to answer these questions. Such a trial will need to be conducted over several years and incorporate objective and subjective data beyond the VSS and UNC4P used in this study.
Discussion
In this prospective, before-after cohort study, we provide long-term data supporting the hypothesis that laser treatments significantly improve the objective and subjective characteristics of hypertrophic burn scars. Using provided-rated and patient-reported instruments, we demonstrated that PDL, CO2, and other lasers rapidly and perhaps permanently lower both VSS and UNC4P, 2 scar assessment tools that measure the thickness, redness, pigmentation, itching, pliability, and pain of hypertrophic burn scars. At more than 2 years of follow-up, VSS had dropped from 10.43 to 3.29, whereas UNC4P had fallen from 5.40 to 1.74. These results were achieved after an average of 5.3 sessions per patients (SD 3.4, median 4), with a complication rate of 4.6% per session and extremely rare adverse events, all related to anesthetic issues. Furthermore, our subgroup analysis revealed that both children and adults benefit from both early and late laser treatments, with the greatest gains occurring in laser sessions that occurred less than 18 months after injury. Decay curve modeling, to account for the natural, incremental improvement of hypertrophic scars, indicates that laser therapies dramatically shift the curve asymptotically toward lower VSS scores. Laser treatments have the potential to accomplish 2 goals: (1) accelerate the time toward maturation of the hypertrophic burn scar, and (2) lower the final endpoint predicted by nonoperative, conventional management.
The precise mechanism accounting for the effect of laser therapy on hypertrophic burn scars has not been elucidated. In fact, applying heat and light to previously damaged skin may seem to be counterintuitive. Indeed, the potential exists to exacerbate the hypertrophic scarring, if burned areas are treated with the wrong laser, the wrong settings, and in the wrong sequence. Nevertheless, several high-quality systematic reviews, consensus reports, and recent clinical trials strongly support the use of laser- and light-based therapies for the treatment of hypertrophic burn scars.
The rationale use of specific lasers, in a defined sequence, to address specific pathological components, allows the provider to manipulate the hypertrophic burn scar and improve specific characteristics such as thickness, redness, and stiffness, which in turn improves the subjective findings of texture, itching and pain, and pliability. Through selective photothermolysis, the 595-nm PDL targets the microcapillaries of hyperemic, immature burn scars, coagulating these vessels and turning off some of the inflammatory component. Once the scar is more mature, the 10,600-nm CO2 laser is next used to target water in abnormal collagen, several millimeters below the surface of the skin. When applied in a fractional pattern, columns of abnormal scar are ablated, allowing new collagen to form in a controlled manner, with rapid reepithelialization of surface. Recent work suggests that in addition to apoptosis of fibroblasts in these microthermal zones, or "MTZs," the hypertrophic scars undergo upregulation of matrix metalloproteinase 1 with alteration of types 1 and 3 procollagen levels and down-regulation of transforming growth factors and basic fibroblast growth factor. Not only are these changes evident in the MTZs, but the entire thickness of the dermis seems to be affected. These molecular and cellular findings are consistent with the clinical observation that fractional CO2 laser treatments, while ablating only the superficial 0.5 to 2.0 mm of the dermis, improve elements that involve the entire thickness of the dermis, such as pliability.
This study provides convincing evidence that the early benefits, which we previously reported, are maintained or further improved at long-term follow-up. Our previous study indicated that the first session yielded the largest drop in VSS and UNC4P, but additional sessions contributed to incremental, statistical reduction in these scar scores. The clinical value of this finding is that although patients may have a dramatic response after 1 to 2 sessions, subsequent treatments may produce specific improvements in components of the hypertrophic burn scars, such as height, stiffness, pruritus, and even pain. For this reason, we recommended several sessions initially, with our overall treatment plan dependent upon the response of the patient to these laser treatments. With the new data from this study, we believe that treatment beyond our original recommendation of 2 to 4 sessions may be warranted, to improve such objective measures as redness, thickness, color, and stiffness. We speculate that not only does laser therapy improve the physical aspects of the hypertrophic burn scar, but that this new approach might eliminate the need for some surgical procedures or decrease the extent of reconstruction that may be indicated.
With this study's follow-up period of 30 months, we addressed a major shortcoming of the prior study: limited follow-up with unknown long-term outcomes. Although laser treatments improved hypertrophic burn scars over a short time horizon, we now know that these therapies yield results that remain stable over 2 years (UNC4P) or continue to improve (VSS). Clearly, laser treatment accelerates scar maturation, clinically, as evidenced by lowering of the decay curve that normally describes the incremental improvement of burn scars, over time. One difference between the long-term follow-up group (30 months) and the short-term cohort (5 months), which must be considered, is that the patients who were tracked over a longer time period had more laser sessions than the group with the shorter follow-up (mean 5.25 vs 2.82 sessions, median 4.0 vs 3.0 sessions). This is not surprising, but these extra sessions must be factored into the interpretation of the final outcomes, apparent at the end of the study period. At the very least, one can conclude that additional sessions effect additional improvement; this was apparent for VSS but not necessarily UNC4P, the latter of which remained stable. In neither case did the objective nor subjective measurements drift back or return to baseline. Scars continued to improve, remained stable, and did not worsen.
Although this project represents the largest, before-after cohort study to date, with long-term follow-up of more than 2 years, this study still has legitimate limitations that will be addressed in future clinical trials. First, not all patients treated in 2011 were available for follow-up in 2013, limiting the sample size of our final cohort. Nevertheless, we were able to demonstrate statistical improvement in hypertrophic burn scars in the smaller cohort, at 30 months of follow-up. Second, both VSS and UNC4P do not provide enough detail to personalize treatments, based on which scars might benefit from certain lasers. In the future, clinical trials will need to include more objective metrics, such as scar thickness documented by ultrasound, degree of rubor determined by a chromometer, and elasticity measured by a curtometer. Furthermore, both burn-specific and nonburn instruments, such as the BSHS-B and SF-36 or SF-12, will be necessary to more accurately determine quality of life. Third, even though the evaluators were blinded to previous scar scores and treatment parameters, the evaluators still carried a bias in favor of the success of this project, potentially influencing the grading of the scars by both provider and patient. Fourth, this before-after cohort study did not include a control group that received only medical therapy, thereby preventing the investigators from determining the observed, natural history of these scars, which tend to improve over time. Fifth, the order of using different laser therapies was not examined and may have a profound impact on final outcomes. To address these issues, the authors recognize that a blinded, randomized, multiple-arm, controlled trial will be necessary to answer these questions. Such a trial will need to be conducted over several years and incorporate objective and subjective data beyond the VSS and UNC4P used in this study.
