Treatment of Hypertrophic Burn Scars with Laser Therapy: A Review of Adverse Events

Abstract

Hypertrophic scarring, characterized by excessive scar tissue formation, is a debilitating outcome that significantly impairs physical and psychosocial recovery following burn injury. Hypertrophic scarring affects a substantial proportion of burn survivors, with reported prevalence as high as 70%. Fractional CO₂ Laser Therapy (FCL), a therapy commonly utilized in acne scar treatment or skin rejuvenation, has become popular in treating hypertrophic scars. Little is known regarding FCL’s adverse events for burn scar treatment. We hypothesize FCL is a safe treatment modality with minimal adverse events in the management of hypertrophic burn scars. This is a retrospective chart review of adverse events after FCL at two centers within a single institution. Burn patients undergoing FCL between May 1^st, 2019 and June 1^st, 2021 were included. Demographics, injury etiology, laser treatment details, and adverse events were collected. A total of 170 patients, 77 (45.3%) males and 93 (54.7%) females underwent 544 FCL therapies for burn scars. Average number of treatments per patient was 3+/−2.23, with a range of 1 to 17 sessions. From the total 544 laser therapy sessions, 13 (2.4%) adverse events were reported. There were five (0.9%) reports of increased post-procedural pain and one (0.2%) report of increased paresthesia/numbness to laser site. Three (0.6%) instances of increased erythema and four (0.7%) reports of epidermal sloughing or blistering were reported. All but five (2.9%) patients reported improvements to scar symptoms. This study demonstrates minimal adverse events associated with FCL for hypertrophic burn scar treatment.

Introduction:

Hypertrophic scarring is characterized by an excess inflammatory response and disorganized collagen deposition after tissue injury.^{1, 2} Histologically, hypertrophic scars form from an overabundance of type III collagen which are organized with nodules of extracellular collagen filaments and myofibroblasts.² These scars form in response to trauma such as burn injury and significantly impair physical function and quality of life. Furthermore, hypertrophic scars affect a significant proportion of burn survivors, with a reported prevalence as high as 70%. It is important for burn providers to effectively monitor and treat hypertrophic scars to minimize its impact on physical and psychosocial well-being during burn recovery.

Common adverse events associated with hypertrophic scars include increased scar stiffness, dyschromia, pruritis, and pain.³ Consequently, there is strong demand for hypertrophic scar prevention and treatment. A recent study reports 91% of patients surveyed value even minimal cosmetic improvements to their scars.⁴ However, despite various available treatment modalities, there is no consensus regarding a gold standard.^{5, 6} Scar treatments include silicone sheeting, pressure garments, topical pharmacological management, and surgical excision. Efficacy of silicone sheeting and pressure garments rely on daily, extended patient compliance.^{7, 8} Surgical excisions of scars are associated with high recurrence rates and are invasive in nature.^{9, 10} However, ablative and non-ablative laser therapy have become increasingly popular therapies for scar management.

Non-ablative laser therapy such as pulse dye laser (PDL) utilize selective thermolysis for scar treatment and may be efficacious in improving scar characteristics such as texture, pigmentation, and pliability.¹¹ Ablative laser therapy such as Fractional CO₂ laser (FCL) utilize energy transfer principles to create specific areas of therapeutic healing by reducing proinflammatory cytokines and inducing alterations in scar collagen composition.¹¹ This fractional photo-thermolysis has been shown to potentially reduce scar thickness, improve pliability, and dyschromia. Significant improvements in scar appearance, tightness, and pruritis have been shown in patients undergoing FCL for scars after burn injury.³ However, optimal timing of intervention, timeline, and laser treatment settings for scar management have yet to be elucidated.

FCL does increase the risk of exacerbating the scar hypertrophy due to the mechanism of administering controlled thermal damage to induce scar remodeling. Large scale studies describing the safety profile of laser therapy for scar management do not exist. Anecdotal adverse events, such as increased dyspigmentation and epidermal sloughing, have been reported but the frequency and characteristics of these events during laser therapy for burn scars are not well studied.¹² Additionally, laser therapy often requires several treatments for maximal effect. Better characterization of the types and rates of adverse outcomes would benefit both physicians and patients when deciding scar treatment therapy. This study characterizes a cohort of patients undergoing scar management therapy with FCL therapy at a single center to determine incidence and further describe adverse events. We hypothesize there to be minimal adverse events associated with FCL therapy for burn scar treatment.

Methods:

This is a retrospective chart review of all patients treated with FCL for scar management at two centers between May 1^st, 2019 and June 1^st, 2021. Data was collected and reviewed from the electronic medical record (EMR) after obtaining approval from our institutional review and ethics board. Inclusion criteria consisted of patients who underwent evaluation for laser treatment and at least one laser therapy session, of which FCL was utilized. Exclusion criteria consisted of patients who received evaluation for laser treatment, but did not receive laser therapy, patients undergoing exclusively laser therapy other than FCL, and patients undergoing FCL for indications other than scar treatment.

Data on patient demographics collected included: age, gender, ethnicity, primary language, employment, comorbidities, insurance status, etiology for scar formation, timeline and number of laser treatment sessions, changes in patient reported scar characteristics, and any adverse events. Qualitative patient descriptions of scar characteristics before and after laser treatment were collected from EMR data. Determination of keloid versus hypertrophic scars was provided by plastic surgeons. Patient outcomes were assessed and collected by three plastic surgeons in follow-up clinic visits at both study locations. Patient selection for laser therapy, timing of interventions, frequency of follow up and laser therapy, and number of treatments were determined through clinical judgement by plastic surgeons. Adverse events in this study were defined as harmful or negative outcomes in patients occurring after laser treatment.¹³

Regarding laser treatment, an ablative, fractional Lumenis UltraPulse CO2 laser 10,600 nm (Yokneam, Israel) is used at both sites. A first pass for all scars is set on DEEP FX at 5% density, 600 hz, 35 mJ of energy. The energy level is then titrated so that minimal punctate bleeding is achieved to a maximum of 50 mJ. A second pass with the SCAAR FX set at 1% density, 120 mJ, 300 hz is used for deeper penetration for scars with thickness greater than 2mm. Following the procedure, a solution of triamcinolone 400 mg per 10 ml is immediately applied. Laser treatment areas are covered with mupirocin 2% ointment and an occlusive petrolatum gauze (Figure 1). Patients are instructed to leave the dressings on for a total of 24 hours at which point they can remove the dressings and shower.

Figure 1.

Standardized Protocol for Fractional CO2 laser for Burn Hypertrophic Scars

Results:

Demographics

A total of 170 patients undergoing 544 laser therapies were included. Demographic results are summarized in Table 1. There were 77 (45.3%) males and 93 (54.7%) females. The average age was 26.4 years (standard deviation (SD): 21.0). Ninety-six (56.5%) patients identified as Hispanic or Latino, 25 (14.7%) patients as Non-Hispanic White, 18 (10.6%) patients as Black or African American, 18 (10.6%) patients as Asian, and 13 (7.6%) patients as Other, Non-Hispanic. Regarding preferred language, 114 (67.1%) patients preferred English, 51 (30.0%) patients preferred Spanish, and five (2.9%) patients preferred some other language. Of the total cohort, 35 (20.6%) patients were employed at time of index laser therapy, 51 (30.0%) patients were not employed or retired, three (1.8%) patients were students, and 81 (47.6%) patients had unknown employment status. One hundred sixty-seven (98.2%) patients were insured at time of laser therapy and three (1.8%) patients were not insured.

Table 1.

Basic Patient Demographics

Characteristics	N=170
Age, mean years (S.D.)	26.4 (21.0)
Sex, n (%)
Male	77 (45.3%)
Female	93 (54.7%)
Race/ethnicity, n (%)
Non-Hispanic, White	25 (14.7%)
Black	18 (10.6%)
Hispanic	96 (56.5%)
Asian	18 (10.6%)
Other, Non-Hispanic	13 (7.6%)
Preferred Language, n (%)
English	114 (67.1%)
Spanish	51 (30.0%)
Other	5 (2.9%)
Employment, n (%)
Yes	35 (20.6%)
No/Retired	51 (30.0%)
Student	3 (1.8%)
Unknown	81 (47.6%)
Insurance, n (%)
Insured	167 (98.2%)
No insurance	3 (1.8%)

Scar Characteristics

Table 2 summarizes the reported scar characteristics of this cohort. All 170 patients presented with hypertrophic scars after burn injury. A total of 53 scars were on the face and neck, 63 scars on the chest/shoulders, 18 scars on the back/flank, 26 scars on the abdomen, 11 scars on the genitals/perineal/buttock, 89 scars on the upper extremities, 81 scars on the lower extremities, 34 scars on the hands, and 14 scars on the feet. Three (1.8%) patients developed scars after both burn and other traumatic injuries.

Table 2.

Scar Characteristics

Patient presenting with Scar Type, n (%)
Hypertrophic	170 (100%)
Keloid	0 (0%)
Scar Location and Number (n)
Face and Neck	53
Chest/Shoulders	63
Back/Flank	18
Abdomen	26
Genitals/Perineal/Buttocks	11
Upper Extremity	89
Lower Extremity	81
Hand	34
Feet	14
Etiology of scar, n (%)
Burn	167 (98.2%)
Burn and other Trauma	3 (1.8%)
Scar Measurement, mean (SD)	34.4 cm2 (77.4 cm2)
Patient Reported Scar Characteristics*, n
Contractured/Distorting local structures	51
Hyperemic	30
Thickened/Raised	61
Hypopigmentation	20
Hyperpigmentation	37
Open areas	5
Number of Patient Reported Scar Symptoms, n
Itch	89
Complaints regarding Appearance	82
Tightness	72
Paresthesia/numbness	10

^*:Patient reported descriptions of scars

Average scar measurement when provided was 34.4 cm² (standard deviation (SD): 77.4 cm²). On initial consultation for laser therapy, 51 scars were described as causing contracture, 30 scars were described as hyperemic or red. Sixty-one scars were described as thickened or raised, 20 scars were hypopigmented, 37 scars were hyperpigmented, and five scars had open areas. At initial laser therapy consultation, there were 89 complaints of itch, 82 complaints of tightness, 72 complaints regarding appearance, and 10 complaints of paresthesia or numbness.

Laser Therapy Outcomes

Between May 1^st, 2019 and June 1^st, 2021, 170 patients underwent a total of 544 FCL treatments. Table 3 summarizes results of laser therapy outcomes. On average patients underwent three laser therapy sessions (mean 3.2, SD: 2.2). The highest number of treatments undergone by a single patient was 17. For all laser therapies, there were no intra-operative complications. General anesthetic was utilized for all surgeries. No standard post-operative anti-bacterial or anti-viral prophylaxis was routinely prescribed. After laser therapy, performing surgeons reported that 165 (97.1%) patients had minimal estimated blood loss (EBL), with minimal EBL defined as estimated total intraoperative blood loss less than 5 mL for all their laser therapy sessions. Of the five (2.9%) patients with EBL greater than 5 mL, all had some other intra-operative procedure during the same time as laser therapy, such as fat grafting, scar excision, or split thickness skin grafting.

Table 3.

Laser Therapy Outcomes

Total Number of Laser Therapies, n	544
Estimated Intra-operative Blood Loss, n (%)
<5 mL	165 (97.1%)
>5 mL	5 (2.9%)
Average Total Laser Sessions, mean (SD)	3.2 (2.2)
Patient Reported Laser Therapy Outcomes, n (%)	129
Improved	121 (93.8%)
No Change	5 (3.9%)
Worse Change	3 (2.3%)
Adverse Events Reported, n	13
Erythema	3
Pain	5
Epidermal Sloughing/Blister	4
Paresthesia/Numbness	1

Regarding patient perspectives, 55 (32.4%) patients reported some degree of improvement in at least one aspect of scar characteristics, such as pain, tightness, itch, appearance, or pliability after their first laser therapy session. Eighteen (10.6%) patients reported no noticeable changes to scar characteristics after their first laser therapy session. Four (2.4%) patients reported some adverse event after first laser therapy session, with three complaints of increased pain and one of paresthesia to laser site. Although patients were counseled at least three sessions were required for laser therapy, 35 (20.6%) patients underwent one laser therapy session before discontinuing therapy.

After all laser therapy sessions, 129 (75.9%) patients provided feedback regarding scar characteristics after laser therapy (Table 3). Of the 129 patients, 121 (93.8%) patients reported improvements to scar characteristics such as pliability, thickness, or pigmentation. Five (3.9%) patients reported no improvements to any scar characteristics. From the total 544 laser therapy sessions, a total of 13 (2.4%) adverse events were reported. There were five (0.9%) reports of increased post-procedural pain. Of patients experiencing post-laser pain, one required a local scalene block. Otherwise, the increased pain was reported to self-resolve or be adequately controlled with medication such as hydroxyzine-hydrochloride 25 mg or hydrocodone and acetaminophen 5–325 mg. No patients required admission for pain control. There was one (0.2%) report of increased paresthesia and numbness to laser site, which self-resolved. Three (0.6%) instances of increased erythema and four (0.7%) reports of epidermal sloughing or blistering at laser site following laser procedure were reported. Regarding those experiencing epidermal sloughing, no changes to the standardized treatment protocol described in the methods were reported. Six patients with adverse events reported improvements in other scar characteristics, for example a patient with blistering reported significant improvements to scar height and pliability after the blisters resolved. A photograph of post-laser blistering is provided in Figure 2.

Figure 2.

Example of Blistering Adverse Event after Laser Therapy

A cohort of patients faced significant barriers to receiving successive laser therapies. There were two (1.2%) patients who declined further therapy due to cost of copay and difficulties with insurance coverage. Four (1.9%) patients/caregivers declined further intervention citing anesthesia risk, five (2.4%) patients required rescheduling on day of surgery due to malfunctioning laser equipment. Fourteen (8.2%) patients opted to delay successive laser therapies due to concerns with COVID-19 surges and 71 (41.8%) patients were pending further scheduling or pending following up at the time of study conclusion. A cohort of 16 (9.4%) patients declined further treatments even if further laser therapies were recommended, citing adequate satisfaction with outcome.

Discussion:

To better define the safety profile of laser therapy, this study investigates adverse events experienced by a cohort of patients undergoing therapy for burn scar management. Although several studies report laser therapy’s efficacy in improving scar characteristics such as itch and tightness exist, few discuss adverse effects.^{14, 15} For example, a recent systematic review investigating the efficacy of FCL found only four studies reported adverse events.¹¹ Of these four studies, two studies reported single incidents of biopsy site infection and allergic contact dermatitis secondary to surgical disinfectant, adverse effects not directly associated with laser therapy.¹¹ The remaining two studies reported minor adverse effects ranging from hyperpigmentation to increased pruritis with no major adverse events.¹¹ Further, little to no literature exists focusing on describing the incidence of adverse events following laser therapy for the management of burn scars. To date, our study of over 500 laser treatments is of the first to primarily quantify and investigate adverse events. The purpose of our study to is to have a more informed discussion with patients about the treatment of hypertrophic scars with laser therapy.

Laser therapy’s therapeutic benefit involves applying a controlled amount of heat and light energy to scars to ablate abnormal scar composition and induce normal wound healing.¹⁶ However incorrect application of therapy, whether in factors such as the amount of energy utilized or frequency of sessions, may lead to worse scar characteristics such as dyschromia or post-operative pain. In our study, of patients experiencing adverse events such as pain or increased pruritis, many reported these to be minimal as these adverse events resolved without intervention and did not affect quality of life. Regarding post-procedure pain, prescription of pain medication was not part of our center’s post-treatment algorithm and was rarely indicated in this cohort. Further, the majority of patients reporting adverse events chose to continue with laser therapy, citing improvements to scar characteristics outweighed potential negative outcomes. Additionally, patients initially experiencing increased scar tightness or pain to laser sites after laser session reported in subsequent follow-up visits that these adverse events were short-lived.

Our findings expand upon existing descriptions of adverse events associated with laser therapy. In one study in which the majority of participants underwent PDL for burn scars, pain (8.1%) and blistering (8.1%) were reported to be the most common adverse events with adverse events such as infection (0.7%) or dyspigmentation (3.0%) as more rare.¹⁷ The majority of patients in our study underwent FCL, expanding literature describing adverse events associated with different laser therapies. Our review of over 500 laser treatments for adverse events reinforce existing limited literature regarding adverse effects associated with FCL in treatment of atrophic acne or non-hypertrophic scars.^{18, 19, 20}

We report adverse events associated with laser therapy are similar to those associated with other non-invasive scar treatment modalities. Common adverse events associated with silicone therapy include contact dermatitis, pruritis, or skin maceration.²¹ Intralesional 5-fluorouracil injections have been associated with pain, hyperpigmentation, and skin sloughing.²² Patients may expect more serious adverse events with laser therapy than those associated with non-invasive treatments such as silicone sheeting or intralesional steroid injections. However, patients should be counseled adverse outcomes with laser therapy are more similar to those of less invasive techniques. Furthermore, with a better understanding of these adverse events, existing recommendations such as utilizing ice packs post-operatively for symptomatic relief can be encouraged for this patient population.^{23, 24} This understanding will allow for more in-depth, informed decision making as patients and physicians develop treatment strategies for burn scar management.

Additionally, patient expectations may also play a significant factor in reported adverse events. Maximal effect of laser therapy may require 4–6 sessions with adequate recovery length in between procedures.²⁵ Several patients in our study expressed disappointment regarding lack of improvements to scar characteristics after laser therapy. Thirty-five (20.6%) patients chose not to continue with laser therapy after one session. Reasons for declining successive laser sessions in this cohort included citing satisfaction regarding treatment with no further desire to address scar characteristics, lack of perceived improvements, or encountering adverse events such as pain or blistering. Patients and surgeons need to have frank discussions regarding expectations and recommendations prior to therapy.

In several cases, instances of scar pruritis and pain were initially reported as adverse events after laser sessions. However, upon further review of the patient EMR, we found these scar symptoms were present prior to therapy, and sometimes reported as even more symptomatic. In these cases, we determined that these were not adverse events associated with laser therapy. In this study, these adverse events were rather classified as laser therapy failing to improve scar symptoms. Regarding reports of increased or unchanged pruritis after laser therapy, further investigation is necessary to determine to what degree these reports were influenced by patient expectations. Managing patient expectations of post-laser scar symptoms, especially after one laser treatment session, is important in delineating adverse events from expected results.

A strength of this study was in the standardization of laser therapy offered to patients and the outcomes measured. This study included two centers utilizing the same laser settings and post-operative management for all laser therapy patients. This reduced bias and variability in our results. However, as many different laser treatments and modalities exist, this also may impact external applicability. Limitations included study design as a retrospective review. Furthermore, due to the lack of quantitative characterization before and after intervention, statistical analysis of treatment and adverse events was not possible. Furthermore, patients lost to follow-up were excluded from this study’s analysis, potentially impacting an accurate characterization of adverse events following laser treatment for burn scars.

Future directions involve investigating adverse events associated with different laser treatment settings or post-operative care algorithms should be studied. Additionally, future studies should investigate the effect of combining laser therapy with other modalities like silicone sheeting or surgical excision on adverse events, as this likely would be most effective in scar management. Furthermore, the safety profile of other laser therapies, such as pulse dye laser, should also be examined and compared to FCL. Studies may also aim to determine optimal intervals between laser therapy and laser settings for specific scars to decrease the risk for adverse events. Lastly, given existing differences in scar formation among ethnic and racial groups, further studies should determine whether these factors affect the likelihood of adverse events and whether modifications to treatment protocols are necessary.

Conclusions:

In this study, patients undergoing laser therapy for scar management reported minimal adverse events, of which the most common were increased pain and erythema to laser site. Subjective improvements were reported after therapy in the majority of patients. Laser therapy is an effective modality with a robust safety profile. This review allows more informed discussions with patients regarding risks of laser therapy for scar management.