The patients themselves assessed the improvement in the treated part as follows: very satisfied in 10 (50%) patients, satisfied in eight (40%) patients, and slightly satisfied in two (10%) patients. For the control part, two (10%) patients were satisfied, seven (35%) patients were slightly satisfied, and 11 (55%) patients were unsatisfied. Accordingly, there was significant patient satisfaction in the treated parts compared with the untreated ones (<0.001).
Safety and tolerability
Post-treatment side effects after each session included erythema, edema, and dark crusts, which resolved within 7–10 days after treatment with removal of the dark crusts. There was mild pain during the laser session, which subsided shortly after the session in 18 (90%) out of 20 cases and lasted several hours to 2 days in the remaining two (10%) cases. Hyperpigmentation and hypopigmentation occurred in two (10%) patients and one (5%) patient, respectively, after the last session and disappeared 3 months after the last laser session. No side effects were noted 3 months after the last session in the treated parts. However, only in the untreated areas, hypertrophic scars were apparent in eight (40%) patients (Fig. 1).
In untreated parts, flattening of the epidermis was prominent in 18 (90%) patients. Meanwhile, treated parts showed a normal epidermis with well-developed rete ridges in 15 (75%) patients (Figs 2–4).
Collagen fibers (Masson trichrome)
There was a significant improvement in collagen fibers (0.002), which became fine and well organized and parallel to the epidermis with decreased interfibrillary spaces in the entire dermis in the treated parts of 15 (75%) patients and the untreated parts in five (25%) patients. The rest of the untreated parts (15 biopsies, 75%) showed fairly thickened hyaline bundles, either disorganized (seven biopsies, 35%) with increased interfibrillary spaces in the entire dermis or randomly within nodules (cigar-shaped) in the middle and deep dermis with some parallel fibers to the epidermis outside the nodule in the superficial dermis (eight biopsies, 40%) (Figs 2 and 3, Table 2).
Elastic fibers (Orcein stain)
There was dense elastotic material throughout the entire dermis in 16 (80%) untreated parts and six (30%) treated parts. Meanwhile, the treated areas of 14 (70%) patients showed a significant improvement (0.001) with less elastotic material and appearance of newly synthesized elastic fibers, which became finer and well organized (Fig. 4 and Table 2).
Histometric evaluation of epidermal thickness
After treatment, the epidermal thickness of the treated part ranged from 65.19 to 79.99 (mean, 70.81±3.32 µm), with a significant increase compared with the untreated part (range, 46.13–62.99; mean, 55.15±4.76; P<0.001) (Fig. 5 and Table 2).
Skin injuries because of trauma or surgery are relatively common, and patients are very concerned about scar formation. Although normal wound healing and scar remodeling continue to occur until 2–3 years after surgery 11, many patients prefer treatment of scars as soon as possible 1, especially when they are located on visible sites 7. Moreover, focus has recently been directed toward early laser treatment for scar prevention to yield better cosmetic results 1.
Specifically, early surgical scars have been treated successfully using a pulsed dye laser (PDL) on the day of suture removal 12, a 1550-nm fractional Erbium glass laser on new thyroidectomy scars 13, fractional ablative 2940 nm Er-YAG in combination with PDL 14, and fractional ablative 10 600 nm CO21,7,8. Meanwhile, on review of the literature, there were no studies discussing the safety of a fractional ablative CO2 laser and the treatment guidelines in patients with dark skin types. Moreover, there were no evidence-based publications discussing its effect at the histopathological level in terms of tissue remodeling during the early postoperative period. Accordingly, the aim of the present study was to assess the clinical efficacy and safety of a fractional ablative CO2 laser in the prevention of postoperative scars in dark skin types, with evaluation of its histopathological effect.
In the present study, a fractional ablative CO2 laser was used during the early postoperative period (2–3 weeks after surgery) on one part of the wound, leaving the rest untreated, serving as a control. We chose this timing of treatment because re-epithelialization would be complete at this point and treatment initiation at this point of time was shown to yield positive results in previous reports 1,8. Moreover, this timing occurred after the end of the inflammation phase of wound healing (4–6 days) and was either in the late proliferative phase of wound healing (4–14 days), where fibroblasts migrate into the wound site and start producing collagen 15, or in the early remodeling phase, which starts roughly at day 8 after the injury and lasts for over a year 16, and during which the extracellular matrix is dynamic, balanced between synthesis and degradation 17.
Six fractional CO2 laser sessions, at 2-week intervals 1, were performed using a pulse energy of 30 mJ. Meanwhile, Lee et al.1 performed two sessions using a fractional CO2 laser, but with a high pulse energy of 80 mJ. Moreover, Jung et al.8 performed one session of fractional CO2 with a pulse energy of 50 mJ on patients with thyroidectomy scars. These previous two studies were carried out on Asian patients with Fitzpatrick skin types III and IV. Meanwhile, this study applied more number of sessions with low fluence on facial wounds of Egyptian patients with Fitzpatrick skin types III to V to ensure efficacy while avoiding prolonged erythema and permanent pigmentation as Egypt is characterized by a sunny climate. Moreover, the scanner size was adjusted according to the length and width of the scar, with an increase in its size about 2 mm all around the scar to stimulate collagen remodeling from healthy skin around wounds.
After 3 months of the last laser session, there was a significant improvement in the total VSS score of the treated parts in addition to significant patient satisfaction compared with the untreated ones. This is in agreement with Lee et al.1 Moreover, Hong et al.7 and Jung et al.8 found a significant decrease in the mean total VSS after treatment with a fractional CO2 laser compared with the baseline state only without involvement of the control untreated part.
In the subset analysis of VSS, there was a significant improvement in pliability and height scores in treated parts, with no significant difference in vascularity and pigmentation compared with the untreated parts. This is in agreement with Lee et al.1. Meanwhile, Kim et al.14, who used both PDL and an Er-YAG laser, found that the best response was found in pliability. Meanwhile, Hong et al.7 and Jung et al.8, using fractional CO2 in early scars, reported a total VSS score without describing its four components separately.
A fractional ablative CO2 laser enables treatment of scars with fewer side effects and less downtime than traditional CO2 lasers 1,6,8,18. This was evident in the present study, where post-treatment mild pain, erythema, edema, and dark crusts were transient and resolved within 7–10 days after each session with removal of the dark crusts. The pain subsided shortly after the session in 90% of the patients and lasted several hours to 2 days in 10% of the patients.
In terms of the pigmentation abnormalities detected in treated parts of the scars in this study, hyperpigmentation and hypopigmentation were observed in two (10%) patients and one (5%) patient, respectively, after the last session and disappeared spontaneously 3 months after the last session. This is similar to Lee et al.1 and Jung et al.8, who observed transient post-treatment hyperpigmentation in one patient and two patients, respectively, on the treated area of the scar. Meanwhile, Chapas et al.19 detected permanent delayed-onset hypopigmentation, which can markedly detract from overall clinical outcomes.
In this study, hypertrophic scars were apparent in the untreated parts only in eight (40%) patients. Meanwhile, Lee et al. 1 observed hypertrophic scarring in one patient on both treated and untreated parts of the scar. Therefore, it is difficult to state that the fractional laser was the sole cause of the scar elevation, although the treated side became thicker and wider than the untreated side, and thus the risk of developing hypertrophic scarring after fractional CO2 treatment cannot be excluded. They recommended using low power (<80 mJ).
Generally, collagen fibers form a network with elastic fibers resulting in a highly ordered structure in the dermis. Meanwhile, collagen is considered the main structural and most abundant extracellular matrix component of the dermis, and plays an essential role in the strength and elasticity of healthy skin and scar tissue 20. In contrast, elastic fibers compose only 1–2% of the dermis and they are critical to the ability of the skin to stretch and recoil 21. Therefore, it is important to study the remodeling of collagen and elastic fibers during wound healing after early laser therapy.
In this study, there was a significant improvement in collagen fibers, which became fine and well organized and parallel to the epidermis with decreased interfibrillary spaces in the entire dermis in the treated parts of 15 (75%) patients and the untreated parts in five (25%) patients.
The rest of the untreated parts (15 biopsies, 75%) showed fairly thickened hyaline bundles, either disorganized (seven biopsies, 35%) with increased interfibrillary spaces in the entire dermis or randomly within nodules (cigar-shaped) in the middle and deep dermis, with some parallel fibers to the epidermis outside the nodule in the superficial dermis (eight biopsies from hypertrophic scars, 40%). On review of the literature, Oliae et al.22 described the scar histopathologically after 4 months of incision without treatment; the collagen fibers became thicker and denser. Moreover, the state of collagen in untreated hypertrophic scars in this study was similar to that described by Linares and Larson 23, Lee et al.24, and Verhaegen et al.25.
For the elastic fibers, dense elastotic material was found throughout the entire dermis in 16 (80%) untreated parts and six (30%) treated parts. Meanwhile, the treated areas of 14 (70%) patients showed a significant improvement, with less elastotic material and appearance of newly synthesized elastic fibers, which became finer and well organized.
Accordingly, it is important to differentiate between normal healing and abnormal scarring. Normal healing occurs when the newly synthesized collagen is not excessive 26 and organized in a well-organized fine network 17 as a natural process of the remodeling stage of wound healing and the skin has sufficient elasticity not to restrict movements. Accordingly, areas of normal scarring should not be distinct from the surrounding skin 26.
For the epidermis, there was a significant increase in the mean epidermal thickness of the treated parts compared with the untreated parts. Accordingly, the interaction between epidermal keratinocytes and dermal fibroblasts could play an important role in regulating tissue homeostasis and processing scar formation 27.
To the best of our knowledge, this study was the first to examine the state of remodeling of collagen and elastin and epidermal thickness following an early intervention of wound during the early postoperative period.
Some authors have hypothesized about how the laser affects the scar-remodeling phase after trauma or surgery. One hypothesis involves thermal injury to the dermis, where neocollagenesis and remodeling occur 8. Other theories focus on the stimulation of growth factors and cytokines by lasers 28 or the initiation of collagen signaling cascades 29. Meanwhile, earlier intervention can theoretically alter the inflammatory phase of wound healing and alter fibroblast migration, leading to a reduction in the appearance of scars 5.
The fractional CO2 laser was effective, tolerable, and safe in the prevention of postoperative scars, especially hypertrophic types, in dark-skinned patients. Histologically, the collagen fibers became fine and well organized, with rectification of the elastic fiber degeneration in addition to increased epidermal thickness. Accordingly, fractional CO2 could act through remodeling of the dermis to activate deposition of its normal architecture (collagen and elastin) in addition to increasing the epidermal thickness.
Conflicts of interest
There are no conflicts of interest.
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Keywords:© 2017 Egyptian Women's Dermatologic Society
CO2 laser; fractional; postoperative; scar