INTRODUCTION

Acne scars are a direct consequence of an altered wound healing response to cutaneous inflammation. Lesions such as comedones, papules, pustules, nodules, and cysts may cause scarring during resolution. As the severity of scarring is known to increase with prolonged inflammation it is imperative to initiate an early diagnosis and treatment of active acne.

MATERIALS AND METHODS

For the purpose of this narrative review, articles were searched in PubMed using key words of “acne scar,” “surgical modalities for acne scars” along with the names of different modalities used in acne scars such as “subcision,” “TCA CROSS,” “chemical peel for acne scars,” “microneedle radiofrequency in acne scars,” “laser and acne scars,” “dermal fillers and acne scars,” “microneedling and acne scars,” “scar revision surgery and acne scars,” “fat grafting for acne scars,” “punch techniques for acne scars,” “grading of acne scars,” “platelet rich plasma therapy and acne scars,” “microdermabrasion and acne scars,” and “botulinum toxin injection and acne scars.”

Those papers, which were on acne scars in skin of color, were predominantly selected. We tried to cover all the articles related to the modalities in the last 15 years. If required, we also looked at older articles.

CLASSIFICATION OF ACNE SCARS

Scars can heal with a depletion (atrophic acne scars) or net gain (hypertrophic acne scars) in collagen. The classification of scars was initially proposed keeping the therapeutic options in mind.[1] Broadly, acne scars can be classified into atrophic and hypertrophic acne scars. Atrophic scars constitute 80%–90% of all acne scars.[2] Atrophic acne scars have been further divided into ice pick (60%–70% of all), boxcar (20%–30% of all), and rolling scars (15%–25% of all).[3] Often all three types of atrophic acne scars may be present simultaneously in the same patient.

Hypertrophic and keloidal acne scars form as a result of decreased collagenase activity and exuberant collagen deposition.

GRADING OF ACNE SCARS

Acne scars are graded based on four comprehensive parameters.[4] These include scar subtype/lesion counting, subjective self-assessment, global acne scar severity scoring, and quantitative measurement of acne scars based on imaging. For the details, the reader can refer the review by Clark et al.[4]

CLASSIFICATION OF AVAILABLE SURGICAL MODALITIES FOR ACNE SCARS

Different surgical procedures have been used to treat acne scars, and newer modalities are being continuously introduced in an attempt to achieve optimal results. Figure 1 shows the classification of different modalities used in acne scar management.

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Figure 1

Classification of surgical modalities for acne scars

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EVIDENCE GRADING

For this review, the available evidence was evaluated using the Strength of Recommendation Taxonomy (SORT) developed by editors of the US family medicine and primary care journals.[5]

Evidence was graded using a three-point scale based on the quality of methodology (e.g., randomized control trial, case-control, prospective/retrospective cohort, and case series) and the overall focus of the study (i.e., diagnosis, treatment/prevention/screening, or prognosis) as follows:

• I:

  Good-quality patient-oriented evidence (i.e., evidence measuring outcome in terms of morbidity, mortality, symptom improvement, cost reduction, and quality of life)

• II:

  Limited-quality patient-oriented evidence

• III:

  Other evidence, including consensus guidelines, opinion, case studies, or disease-oriented evidence (i.e., evidence measuring intermediate, physiologic, or surrogate endpoints that may or may not reflect improvements in patient outcomes)

Clinical recommendations were developed on the best available evidence tabled in the guideline. The strength of recommendation (SoR) was ranked as follows:

• A:

  Recommendation based on consistent and good-quality patient-oriented evidence

• B:

  Recommendation based on inconsistent or limited quality patient-oriented evidence

• C:

  Recommendation based on consensus, opinion, case studies, or disease-oriented evidence

In those situations where documented evidence-based data were not available or had inconsistent or limited conclusions, expert opinion and the medical consensus was used to generate clinical recommendations.

In this review, level of evidence (LoE) and strength of recommendation (SoR) are mentioned in most of the modalities based on the best available evidence.

CHEMICAL PEELS IN ACNE SCARS

For atrophic acne scars: LoE III, SoR C

For post-acne hyperpigmentation: LoE II, SoR B

The selection of the chemical peeling agent depends on the patient’s skin type and severity of scarring. The most effective treatment outcomes are seen with macular pigmented acne scars. Superficial acne scars (post-acne hyperpigmentation) respond well to 30% salicylic acid peel used in multiple sessions at 4–6 weeks of intervals.[6] Full strength, 92% lactic acid (LA) has shown an improvement in texture and color of pigmented scars in skin type IV and V.[7] Jessner’s solution combined with 35% or 20% trichloroacetic acid (TCA) has shown marked reduction of both ice pick and rolling scars.[89]

The primary concern with TCA is the risk of post-inflammatory hyperpigmentation (PIH), particularly in the skin of color. Moderate acne scars have been found to respond to 40%–70% pyruvic acid (PA) peel.[10] Glycolic acid (GA) is widely used in treating both acne and acne scars. It improves acne scars by increasing dermal and epidermal hyaluronic acid (HA), resulting in remodeling of extracellular matrix.[11]

Several combinations of GA peel along with other modalities have been tried. These include topical retinoic acid, microneedling, and iontophoresis with ascorbyl 2-phosphate 6-palmitate and dl-α-tocopherol phosphate (for improvement in PIH).[1213]

Mandelic acid 10% in combination with salicylic acid 20% (salicylic-mandelic peel, i.e., SMP) has been compared with 35% GA peel.[14] Modest improvement was observed in ice pick scars, boxcars, and rolling scars in both the groups, but the former was safer and more efficacious in PIH. A modified form of phenol peel (Exoderm) has been tried with good improvement, but considerable side effects such as dyspigmentation, prolonged erythema, and milia formation were seen.[15]

Considering their flexibility and low cost of treatment, chemical peels play an important role in the management of all grades of acne scars. Superficial peels such as Jessner’s solution, full strength 92% LA, 20%–70% GA, SMP, and 10%–25% TCA are safe, and multiple sessions can attenuate superficial acne scars in patients with skin of color. Extra caution needs to be exercised with moderate depth (25%–50% TCA, TCA 35% + Jessner’s solution, and 40%–60% pyruvic acid) and deep peels because of the risk of PIH and post-procedure scarring.

CHEMICAL RECONSTRUCTION OF SKIN SCARS

For ice pick scars: LoE II, SoR B

TCA-chemical reconstruction of skin scars (CROSS) involves the serial local application of high concentration TCA with a wooden applicator to the scar.[16] No anesthesia is needed. TCA is applied for a few seconds until the scar displays a white frosting. A black crust forms in 3–4 days and heals in 7–10 days. The clinical effects of TCA are due to dermal collagen remodeling and an increase in the content of collagen, glycosaminoglycan, and elastin.

Varying concentrations of TCA ranging from 35% to 100% have been used. Good to excellent improvement has been reported in approximately two-third to three-fourth patients, depending on types and grades of scars. Approximately a third patients with darker skin type may develop PIH, which may persist in some patients.[1718] Better results are observed with 100% compared to 65% TCA CROSS.[19] Phenol (88%) has been used in place of TCA (90%) with comparable results in V and VI skin type.[20] TCA CROSS has been combined with subcision and fractional lasers with good improvement.[2122] There are studies comparing microneedling with TCA CROSS. Boxcar and rolling scars responded well to microneedling and ice pick scars to the CROSS technique.[23] Ramadan et al.[24] found TCA CROSS to be inferior to subcision in decreasing the size of scars with TCA having more pigmentary alteration. It has been found to have comparable efficacy with 1550 nm Er:glass fractional laser in patients of type IV and V skin. Rolling scars had superior outcomes with laser, whereas ice pick scars had similar improvement with both techniques.[25]

DERMABRASION

Superficial and small scars: LoE II, SoR B

Dermabrasion is a sequential removal of the skin layers to the desired level, from the epidermis to dermis. The procedure uses a wire brush, diamond fraise, or sterilized common sand paper and is performed under topical or infiltration anesthesia. After surgical cleansing, the scars are marked with the patient in sitting position, the skin is stretched and dermabrasion is performed up to the base of the scars, but not deeper than the junction of the upper and mid-reticular dermis. Crusting can last 7–10 days, depending on the depth of dermabrasion, and reepithelialization occurs from cells within the adnexal structures. Infections, persistent dyschromia, hypo- or hyperpigmentation, erythema, and scarring are possible complications. Dermabrasion is particularly successful in treating superficial atrophic acne scars, such as rolling or boxcar scars.[26] Strict sun protection is essential for the prevention of PIH, particularly in darker skin types.

MICRODERMABRASION

Mild to moderate scars: LoE II, SoR B

Microdermabrasion is a superficial variation of dermabrasion, which only removes the outer layer of the epidermis. It is a minimally invasive technique of mechanical abrasion of the skin, which accelerates the natural process of exfoliation.[27] Earlier, the handpiece made use of aluminum oxide or sodium bicarbonate crystals for abrasion, whereas now diamond tips are commonly used to increase accuracy and decrease irritation. Post-procedure hyper- or hypopigmentation, and hypertrophic scarring are the potential complications, particularly in Fitzpatrick skin type IV and VI.[28]

In moderate to severe acne scars, satisfactory results are seen in only approximately 5%–20% of patients. Priming with topical adapalene 0.1% 2 weeks before the procedure can improve the outcomes. Bhalla[29] reported comparable results with microneedling and microdermabrasion. Most studies reported good improvement in around 50% of the grade 2 scars and 20% of the grade 3 scars, whereas no response was seen in grade 4 scars.[30]

MICRONEEDLING

Mild to moderate scars: LoE I, SoR A

Microneedling is a minimally invasive therapeutic modality, involving superficial and controlled puncturing of the skin by miniature fine needles fitted on a drum-shaped cylinder, which is rolled over scarred skin.[3132] The procedure is performed under topical anesthesia. Each pass produces micropunctures in the stratum corneum, which results in a controlled skin injury. The treatment endpoint is identified as uniform pinpoint bleeding. A wound-healing cascade causes a release of growth factors, leading to neocollagenesis.[33] The needles also breakdown scar strands and allow the area to revascularize.

Dermapen is an electronic microneedling device, which has a detachable head of 33 G size consisting of 12 microneedles that can penetrate to variable depths in the skin, depending on preset values. A comparative study conducted between microneedling by Dermapen versus GA peel versus the combination of both suggests combination to be more effective.[34]

Microneedling is moderately effective for the rolling type of acne scars.[35] All types of atrophic scars tend to improve (in the range of 50%–60%) with microneedling to a variable grade.[36] Afra et al.[37] found the efficacy of microneedling comparable to that of topical tazarotene 0.1% after four treatment sessions. Microneedling has been found to be inferior to Er:yttrium aluminum garnet (YAG) laser in a split face trial by Osman et al.[38]

MICRONEEDLE RADIOFREQUENCY FRACTIONAL

Mild to moderate scars: LoE I, SoR A

Microneedle radiofrequency fractional (MNRF) has been found to be effective in reducing both atrophic acne scars and open pores. As the impedance of the dermis is lower (due to the higher water content) than the epidermis, the flow of energy is greater in the dermal tissue, leading to the formation of a larger coagulative thermal zone.[39] Radiofrequency energy disrupts the dermal fibrotic strands and triggers collagen remodeling.[40] It creates a pyramidal injury zone unlike the conical thermal damage induced by ablative lasers and greater depth of penetration of the microneedles (up to 3.5 mm) as compared to fractional lasers (0.7 mm) [Video 1] [Figure 2]. Insulated microneedle coagulates only the deeper part and protects the epidermis, but it is associated with bleeding. Uninsulated microneedle causes coagulation along the full length of the needle, thus prevents microbleeding.[41] MNRF usually requires 4–6 sessions for optimal results. The majority of patients show only mild to moderate (25%–50%) improvement.[4243]

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Figure 2

Baseline and post-treatment picture of combination of MNRF and SA peel 30% after five sessions

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Comparative studies with lasers have shown similar efficacy. Chae et al.[44] compared MNRF with Er:glass laser in Korean patients. After 20 weeks of follow-up, scar severity scores improved by a mean of 18.6% and 25% in MNRF and Er:glass groups, respectively (P < 0.01).[44] A combination of fractional CO₂ laser with MNRF was found to be better than laser alone.[45] Similarly, studies have combined MNRF with a diode laser, fractional thulium lasers, and bipolar radiofrequency devices with combinations being more effective than monotherapy.

MNRF has minimal adverse effects such as pain, erythema, edema, and spot bleeding. Pain is significantly lower as compared to ablative fractional lasers. It is safe and moderately effective in all types of acne scars in type III and V skin (a color-blind procedure).

LASERS AND LIGHT SOURCES

Laser treatment of atrophic acne scars can be divided into two main categories: ablative and non-ablative. Thermal injury delivered by lasers leads to stimulation of dermal fibroblasts, which initiate new collagen and elastin production. The cosmetic outcome depends on the ability to increase efficacy and reduce downtime and adverse effects associated with these devices.

An overview of lasers available for acne scarring is given in Table 1.

In darker skin types (IV and V), lower energy should be used to minimize PIH. Concurrent isotretinoin treatment is not considered as a contraindication for laser therapy.[46] Lasers should be avoided in areas of active inflammation and infection. Choosing appropriate settings for laser taking into consideration the depth of the scar, skin type, and tendency to PIH is of utmost importance. As the parameters vary considerably between different machines, it is advisable to start at lower fluence and increase gradually guided by the outcomes and adverse effects.

SUBCISION

LoE II, SoR B

Subcision or subcutaneous incisionless surgery is a simple technique for the elevation of depressed tethered scars by the introduction of a sharp needle beneath the scar, which breaks the fibrous adhesions and lifts the scar.[73] It can be carried out using either a Nokor needle or a disposable hypodermic needle. The sharp bevel of the needle acts like a scalpel and incises the fibrous tissue that binds down the scar [Figure 3]. In addition, the needle-induced trauma leads to the formation of connective tissue beneath the scar, without injuring the epidermis.

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Figure 3

Schematic diagram showing cutting of fibrous strands in subcision

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Subcision is most useful for rolling scars but can also help partially in the elevation of ice pick and boxcar scars [Figure 4]. It is contraindicated in patients with a bleeding diathesis as well as those on aspirin, vitamin E, or other drugs prolonging bleeding time as it can cause larger hematomas, leading to the formation of persistent fibrous nodules.

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Figure 4

Improvement in rolling acne scars after two sessions of subcision

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The procedure should be performed under infiltration anesthesia. After surgical cleansing, the needle (18–24 G, depending on the size of the scars) is introduced from the edge of the scar into the dermis moving in a horizontal plane. The bevel faces upward. It is then moved back and forth to cover the entire scar and then moved horizontally in a fanning motion to break all adhesions [Video 2]. The endpoint of subcision is a smooth movement of the needle without any grating sound or resistance and a visible lifting of the scars. Light pressure is given after the procedure to prevent a visible bruise or hematoma. Care should be taken not to penetrate deep and injure the vessels. The temporal and preauricular areas are danger areas as the branches of the facial nerve are superficial. Common complications of subcision include pain, bruising, hematoma, swelling, edema, induration, persistent fibrous nodules, and PIH. In an Indian study, the improvement ranged from 40% to 80% in rolling scars.[74] Alam et al.[75] reported improvement in appearance in 90% of the patients. The mean overall degree of improvement was 51%.

Several modifications of subcision have been described in the literature. One modification is bending the needle at right angles with the help of a sterile artery forceps.[76] This ensures that the plane of subcision remains horizontal. A further modification is that the needle is further bent at right angles and mounted on a syringe; it becomes a convenient and quick method [Video 3].[77] A needle holder can be used to hold the needle to maintain the position of the needle.[78] When a wide area of depressed scars is involved, a diamond-shaped subcision can be made using a sterile aspiration needle, called dermal tunneling.[79] In this technique, the area to be treated is marked in a diamond shape and subcision is carried out from all four corners. Spinal needle cannula has also been used to reduce the number of pricks.[80]

Subcision can be repeated every 2–4 weeks till optimum response is obtained. It has been combined with other techniques, such as fractional CO₂ lasers,[56] microneedling, cryoroller,[81] or PRP,[82] to improve the outcome.

PUNCH TECHNIQUES FOR ACNE SCARS

Moderate to severe scars: LoE III, SoR C

Punch excision techniques are useful for deep depressed acne scars with sharp vertical walls such as ice pick and boxcar scars.[83] These scars extend to the deep reticular dermis and hence cannot be safely treated with resurfacing techniques alone. Punch techniques include punch elevation, punch excision, or punch grafting. In punch excision, the scar is excised and sutured along the relaxed skin tension lines, thus replacing a wide circular scar with a smaller linear scar. In punch grafting, the scar is excised and replaced by dermis from autologous donor tissue. In punch elevation or punch flotation, the depressed scar is lifted from its bed by breaking the adhesions, which bind down the scar [Figure 5].

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Figure 5

Punch elevation in grade 4 acne scars

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If the surface of the scar is atrophic and it is less than 3.5 mm, it is excised out and replaced by a donor punch graft from the postauricular region or gluteal region. If its size is more than 3.5 mm, a punch graft can leave a noticeable ring scar; hence, it is preferable to excise the scar and suture.

The scars that need excision and suturing are tackled first [Figure 6]. In punch excision and grafting, the donor grafts should have a snug fit to prevent a cobblestone appearance. This can be carried out by appropriate trimming of the graft. Grafts can be held in place by surgical glue or Steri-Strips, followed by a nonadherent dressing for 3–5 days. If there are many closely packed scars, the procedure can be performed in two or more sessions.

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Figure 6

Combined punch elevation and punch excision in severe acne scars

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Complications include failure-to-take off graft, graft extrusion, cobblestone appearance [Figure 7], PIH, ring scars at the margins of the punch, or widening of the suture line. Hyperpigmentation can be treated with topical agents, and cobblestone appearance and ring scars by resurfacing.

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Figure 7

Cobble stoning after punch replacement

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It is advisable to combine these techniques with subcision either in preceding sessions or in the same session. Punch excision techniques should be followed by laser resurfacing to optimize results.

PLATELET-RICH PLASMA AND RELATED TREATMENTS

Platelet-rich plasma (PRP) consists of the patient’s plasma that is enriched with a high concentration of platelets. They contain storage pools of numerous growth factors, cytokines, and chemokines. PRP is thought to correct atrophic scarring through the release of growth factors from α-granules. Another pathway that explains the effect of PRP is the generation of HA, which draws water into the matrix, causing it to swell, creating volume, and skin turgor. HA also promotes cell proliferation and extracellular matrix formation thereby modulating the diameter of the collagen fibers, thus improving atrophic scars. PRP has been studied mostly as adjunctive therapy to other treatment modalities like microneedling and fractional ablative laser.

AUTOLOGOUS FAT GRAFTING

LoE II, SoR B

The resolution of nodulocystic acne often results in wide areas of depressed scars with loss of tissue, called lipoatrophic acne scars. These scars are more common in the lower cheeks and mandibular area, giving a gaunt and prematurely aged appearance to the patients. They are best treated by a filling substance such as a synthetic filler or autologous fat (lipofilling). Fillers are short-lived and are expensive. Hence, lipofilling is preferred, which also has the advantage of supplying adipose-derived stem cells, which have an important role in the regeneration of collagen.[92] Previously, boluses of fat were injected (macrofat and microfat), but results were unpredictable as chances of fat necrosis of the central core of fat tissue were higher. The recent technique to process the fat to finer components (nanofat) gives more predictable results.[93]

In this method,[93] fat is harvested either from the lower abdomen or the thigh after tumescent anesthesia. After the preparation of nanofat, it is then injected just beneath the dermis to replace lost tissue volume to get a smooth surface [Video 4]. In the treatment of acne scars, it is essential to do subcision and break all adhesions before lipofilling to prevent irregularities and outpouching of fat. Zichun et al.[94] injected nanofat in 20 patients with atrophic scars and observed significant improvement in the appearance. Azzam et al.[95] compared three sessions of fractional CO₂ laser versus a single session of autologous fat transfer in 22 patients with acne scars. Fat transfer was more effective in scar treatment. However, long-term follow-up was not available.

The advantages of lipofilling are that it is autologous, easy to obtain, minimal donor site morbidity, and large amounts can be harvested and with minimal downtime. It is easily contoured, feels natural, and has regenerative potential. The disadvantages include a variable retention rate and unpredictability; hence multiple procedures may be required.

SYNTHETIC FILLERS

Fillers are commonly used in the treatment of facial tissue augmentation, but their role in the treatment of facial acne scars is yet to be fully exploited. To date, polymethyl methacrylate (PMMA) is the only US Food and Drug Administration (FDA)-approved filler for the treatment of atrophic acne scars, with a large randomized controlled trial, supporting its use. Dermal fillers may be considered for boxcar or rolling atrophic acne scars. There is insufficient evidence to support the use of fillers for deeper ice pick scars. Fillers are injected by various techniques such as linear threading, depot, fanning, layering, and tower to achieve optimum volume augmentation. Commonly used fillers are given in Table 2.

BOTULINUM TOXIN A INJECTION

Hypertrophic scar: LoE III, SoR C

In addition to botulinum toxin’s well-known effect on reducing muscular activity, there also appears to be an inhibitory effect on fibroblasts,[106] thereby, offering a satisfactory outcome for scar treatment.

In a study comprising 26 Chinese patients, acne scars treated with botulinum toxin A injection showed significant improvement.[107]

COMBINATION AND MULTIMODALITY TREATMENTS

Complete resolution of acne scars is a challenge and rarely achieved with the currently available modalities. Combining different treatments, either sequentially or in the same session, has shown to produce better outcomes. The goal remains to effectively exploit different technologies and treatment modalities to tackle post-inflammatory erythema, pigmentation, different types and depths of scars as well as reduce treatment downtime. Many studies have been conducted combining non-ablative lasers with ablative lasers, subcision, TCA CROSS, and PRP, to achieve an additional rejuvenation effect. Subcision has been combined with fractional lasers and microneedling to take care of deeper scars [Figure 8]. PRP has been used widely with many other modalities for better remodeling of scars and reducing post-procedure inflammation. Dermal fillers and autologous fat transplantation can be effectively combined with resurfacing procedures such as lasers or microneedling to achieve both volume restoration and rejuvenation.

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Figure 8

Acne scar treated with two sessions of subcision, six sessions of MNRF and 30% SA peel

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NEWER AND EXPERIMENTAL TREATMENTS

Autologous non-cultured dermal cell suspension

LoE III, SoR C

In atrophic acne scars, the dermis is lost due to inflammation, therefore dermal suspensions could be an ideal volume replacement. Sahoo et al. prepared an autologous non-cultured dermal cell suspension by incubating a de-epithelialized dermal biopsy with collagenase 1. The suspension was then injected to correct localized facial volume loss. This resulted in significant improvement in the dermal atrophy group, but not in the lipoatrophy group [Figure 9].[108]

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Figure 9

Dermal cell suspension in acne scar. (A) Baseline picture. (B) At 3 months showing 50% improvement. (C) At 6 months showing 60% improvement from baseline (Source: Sahoo et al.)

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Jet volumetric remodeling

LoE III, SoR C

Jet volumetric remodeling (JVR) is a needle-free proprietary technology; which accurately delivers kinetic energy and a healing compound at a high speed simultaneously via a tiny entry point in the epidermis [Video 5, Figure 10]. The particles, acting as nano-bullets, disperse in the dermis to create a microtrauma, which promotes neocollagenosis. The JVR device using HA has been used to treat acne scars in two patients in two sessions showing some improvement. There was minimal downtime.[109]

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Figure 10

Pre- and post-treatment picture of combination treatment with subcision, eight sessions of MNRF and one session of JVR

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Radiofrequency subcision

LoE III, SoR C

This modification of subcision uses radiofrequency energy for subcision. This method decreases the chances of postoperative bleeding and hematoma formation. The fibrotic strands get cut with ease without any mechanical force [Video 6, Figure 11].[110111112113114115]

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Figure 11

Improvement in acne scar with radiofrequency subcision

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TREATMENT RECOMMENDATION SUMMARY

Treatment recommendation summary is given in Figure 12.

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Figure 12

Recommendation summary for management of acne scars

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EVIDENCE-BASED RECOMMENDATIONS

Table 3 summarizes the level of recommendations for different procedures for acne scars.

All videos available online www.jcasonline.com