Med Lasers 2024; 13(1): 25-34  https://doi.org/10.25289/ML.24.005
Comparison of the picosecond and Q-switched Nd:YAG lasers in the treatment of pigmentary disorders: a retrospective case series in the Republic of Korea
Sung Joo Byun, Won-Serk Kim, Young-Jun Choi
Department of Dermatology, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea
Correspondence to: Young-Jun Choi
E-mail: reve01@naver.com
ORCID: https://orcid.org/0000-0002-9501-2914
Received: March 5, 2024; Accepted: March 19, 2024; Published online: March 30, 2024.
© Korean Society for Laser Medicine and Surgery. All rights reserved.

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background: A picosecond laser irradiation technique has presented satisfactory cosmetic outcomes for the treatment of various pigmented lesions. We aimed to evaluate the clinical results of a picosecond neodymium-doped:yttrium aluminum garnet (Nd:YAG) (PSNY) laser for the treatment of various pigmented lesions and to compare them with the results of a conventional Q-switched Nd:YAG laser.
Methods: A retrospective review of subjects treated with a PSNY laser was performed. Clinical improvement was assessed by two blinded dermatologists using a 5-point Global Assessment Scale (GAS). Adverse events were also assessed.
Results: Forty-eight patients were treated with a dual-wavelength (532-nm and/or 1,064-nm) PSNY laser. Sixteen of the 48 patients (33.3%) experienced more than 50% improvement after the PSNY treatment. Patients with café-au-lait macule showed the greatest improvement, which was fair to good (GAS, 3.80 ± 0.76). Patients with postinflammatory hyperpigmentation received the highest number of treatment sessions (6.60 ± 3.44 times). The duration of follow-up was the longest in patients with Ota’s nevus (22.50 ± 5.44 weeks). There were no serious complications during the treatment period.
Conclusion: In our case series, it was concluded that a dual-wavelength 532-nm and 1,064-nm PSNY laser was safe and effective for the treatment of pigmented lesions in Korean patients.
Keywords: Asian; Laser therapy; Neodymium-doped yttrium aluminum garnet lasers; Pigmentation disorders; Skin pigmentation
INTRODUCTION

Pigmented skin disease is one of the most common conditions in the Asian population, and it is often very troublesome. In the past decade, several lasers have been developed with wavelengths selectively absorbed by melanin; when pulsed at nanosecond durations, these lasers can effectively treat pigmented lesions. Several of these lasers include the Q-switched (QS) 755-nm alexandrite laser, the QS 532-nm and 1,064-nm neodymium-doped:yttrium aluminum garnet (Nd:YAG) laser, and the QS 694-nm ruby laser. The QS lasers deliver ultrashort pulses in the nanosecond-domain with high peak powers. They emits laser energy at a pulse duration that is shorter than the thermal relaxation time (TRT) of melanosomes and melanocytes, selectively photothermolysing these cells. However, Asian people are susceptible to post-laser treatment exacerbation and certain side effects, especially postinflammatory hyperpigmentation (PIH) [1]. Thus, the management of pigmented disorders in Asian skin is more difficult than in Caucasian skin.

Picosecond-domain lasers (PSLs) have recently been developed to generate a sub-nanosecond (10–12 of a second) pulse duration [2]. In 1998, Ross et al. [3] demonstrated that PSL pulses are more efficient in clearing cosmetic tattoos than nanosecond-domain laser (NSL) pulses. Since that initial study, many published articles have demonstrated effective tattoo removal using various PSLs [4]. PSLs are effective at delivering an optical pulse duration very close to the TRT of tattoo pigment molecules (less than 10 nanoseconds). Thus, these pulse durations can produce the most effective thermal radiation and apply more targeted photochemical damage than conventional NSLs. As has been confirmed in many studies, PSL leads to more specific and confined pigment destruction at lower fluence. Therefore, it is expected that PSL will also be able to treat other pigmented lesions more quickly and safely than NSL [2].

To date, only a small number of clinical studies have demonstrated the clinical efficacy of PSLs for the treatment of benign pigmented lesions in the Asian population [5-7].

In this study, we performed a retrospective photographic and chart review. The aim of this study was to evaluate the degree of clinical improvement and adverse events of various pigmented lesions treated with 532-nm and/or 1,064-nm picosecond Nd:YAG (PSNY) lasers in Asian skin. We then compared the results with previous clinical studies that employed a conventional QS Nd:YAG (QSNY) laser. This is a case series study of the PSNY laser used for the treatment of pigmented lesions other than for tattoo removal.

METHODS
Ethics statement: This study was approved by the Institutional Review Board of Kangbuk Samsung Hospital (Approval No.: KBSMC 2017-01-008). Informed consent was obtained from the participants.

Study design

This was a single-center, retrospective study of the safety and efficacy of a PSNY laser for the treatment of various pigmented skin disorders in Asian skin.

Patients

Korean patients who visited our clinic because of benign pigmented disorders were reviewed over eight months (from December 2015 to August 2016). Clinical information of patients was obtained from digitally-stored medical records including age, sex, duration and number of treatments, laser settings, and complications. Patients had no previous history of malignant neoplasms of the skin, keloid or hypertrophic scarring, connective tissue disease, radiotherapy on affected skin, or photosensitivity. Also, patients had no infections or wounds on the affected skin. Pregnant and breast-feeding females were excluded.

Laser treatment

All patients were treated with only a 750-picosecond domain, dual-wavelength (532-nm and/or 1,064-nm) Nd:YAG laser (PicoPlus4®; Lutronic Co., Ltd.). Before the laser treatment, informed content was obtained. The affected area was treated with 2 to 4 passes of the laser, until the lesions showed mild erythema or whitening. Topical anesthetic cream (a eutectic mixture of 2.5% lidocaine and 2.5% prilocaine; AstraZeneca) was applied to the affected skin with occlusion for 30 minutes before PSNY laser treatment. After the treatment, humectant and sunscreen were applied to the treated lesions.

Comparison between a picosecond laser and a conventional QSNY

Mean total number of treatment sessions, mean energy fluence, and adverse effects of laser treatment using the PSNY laser were compared with those using a conventional nanosecond QSNY laser (SPECTRATM XT; Lutronic Co., Ltd.).

Blinded evaluation of digital images

Clinical photographs were taken before each treatment using a handheld digital camera (Canon EOS 600D; Canon Inc.) under the same conditions. Assessment of clinical improvement was evaluated using these photographs by two blinded dermatologists using a 5-point Global Assessment Scale (GAS; excellent: 75%-100% lesion clearance, score 5; good: 50%-74% lesion clearance, score 4; fair: 25%-49% lesion clearance, score 3; poor: <25% lesion clearance, score 2; worse: results worse than the pretreatment status, score 1).

Adverse events

Patients were asked to report adverse events of the laser treatment. During the follow-up period, complications were recorded on the digital medical record.

RESULTS

Clinical characteristics of the patients

Within the eight-month period, a total of 48 ethnic Korean patients, 38 females and 10 males, took part in this study. The characteristics of the patients at baseline are shown in Table 1. The mean age at the onset of laser treatment was 31.8 ± 21.2 years (range, 1-71 years). Fitzpatrick skin types were mostly type III or IV. The pigmentary disorders consisted of Ota’s nevus (20.8%), melasma (18.8%), lentigines (16.7%), PIH (10.4%), café-au-lait macule (CALM, 10.4%), freckles (6.3%), congenital melanocytic nevus (CMN, 4.2%), melanonychia (4.2%), blue nevus (2.1%), nevus spilus (2.1%), Becker’s nevus (BN, 2.1%), and argyria (2.1%). Most of the pigmented lesions were located on the face (85.4%).

Table 1 . Patient demographics and clinical characteristics

Demographic informationValue (n = 48)
Sex
Male10 (20.83)
Female38 (79.17)
Age (yr)31.8 ± 21.2
Fitzpatrick skin types
III20 (41.67)
IV25 (52.08)
V3 (6.25)
Indications
Ota’s nevus10 (20.83)
Melasma9 (18.75)
Lentigines8 (16.67)
Postinflammatory hyperpigmentation5 (10.42)
Café-au-lait macules5 (10.42)
Freckles3 (6.25)
Congenital melanocytic nevus2 (4.17)
Becker’s nevus1 (2.08)
Blue nevus1 (2.08)
Nevus spilus1 (2.08)
Argyria1 (2.08)
Melanonychia2 (4.17)
Distribution of lesions
Face41 (85.42)
Neck1 (2.08)
Trunk2 (4.17)
Upper extremities2 (4.17)
Lower extremities0
Other2 (4.17)

Values are presented as number (%) or mean ± standard deviation.



PSNY laser treatment

The laser parameters were variable, 532-nm and/or 1,064-nm wavelengths with a fixed pulse duration of 750 picoseconds, spot size from 2.3-10.0 mm, energy density range from 0.3-6.4 J/cm2, and pulse rate from 2-10 Hz. Number of sessions, total duration of treatment, and laser parameters for each pigmented disorder are summarized in Table 2. The highest number of treatment sessions was observed in patients with PIH (6.60 ± 3.44 times). Duration of follow-up was the longest in patients with Ota’s nevus (22.50 ± 5.44 weeks).

Table 2 . Treatment parameters used for the picosecond Nd:YAG laser

IndicationNo. of treatment sessionsMean total duration of treatment (wk)No. of applied lasersWavelength (nm)Spot size (mm)Fluence (J/cm2)Pulse rate (Hz)
Ota’s nevus2-9 (3.70 ± 2.16)13-29 (22.50 ± 5.44)101,0645-9 (5.65 ± 0.98)0.65-4.00 (2.45 ± 1.14)5-10 (8.47 ± 2.34)
Melasma1-8 (3.44 ± 2.55)2-26 (10.10 ± 8.24)91,0648-10 (8.17 ± 0.53)0.30-0.95 (0.72 ± 0.23)10
Lentigines1-4 (2.00 ± 1.20)2-16 (7.75 ± 5.06)75322.3-4.3 (3.20 ± 0.57)0.4-1.5 (0.75 ± 0.81)2-5 (2.30 ± 0.95)
31,06480.8-0.9 (0.84 ± 0.05)10
PIH2-10 (6.60 ± 3.44)16-27 (21.40 ± 4.83)51,0646-8 (7.88 ± 0.49)0.6-1.5 (1.93 ± 0.17)1-10 (9.47 ± 2.09)
CALM1-5 (3.00 ± 1.87)8-23 (15.20 ± 6.91)55323.0-5.3 (3.60 ± 0.73)0.4-0.7 (0.51 ± 0.10)2-5 (3.00 ± 1.50)
31,0646-8 (7.70 ± 0.76)0.7-2.8 (1.10 ± 0.76)10
Freckles1-4 (2.00 ± 1.73)4-19 (9.60 ± 8.14)35323.30.40-0.55 (0.44 ± 0.08)2
21,06480.55-0.90 (0.74 ± 0.15)10
CMN22-10 (7.50 ± 3.54)21,0644-8 (5.80 ± 2.05)0.8-6.4 (3.16 ± 2.47)2-5 (3.80 ± 1.64)
Becker’s nevus2611,06480.95-1.20 (1.08 ± 0.18)10
Blue nevus52115323.30.62
11,0643-5 (4.00 ± 0.71)1.7-6.0 (3.50 ± 1.56)1-10 (4.00 ± 2.00)
Nevus spilus51615323.30.4-0.5 (0.45 ± 0.07)2
11,06480.7-0.9 (0.83 ± 0.12)10
Argyria21211,06480.4-1.0 (0.70 ± 0.42)10
Melanonychia2-3 (2.50 ± 0.71)5-7 (6.00 ± 1.41)21,0644-6 (5.20 ± 0.84)2.0-3.4 (2.68 ± 0.64)5

Values are presented as range (mean ± standard deviation).

Nd:YAG, neodymium-doped:yttrium aluminum garnet; PIH, postinflammatory hyperpigmentation; CALM, café-au-lait macules; CMN, congenital melanocytic nevus.



Comparison of energy fluence used for the PSNY versus QSNY laser in the treatment of benign pigmented lesions is summarized in Table 3. Overall, lower fluence was used in PSNY compared to QSNY in pigmented lesions.

Table 3 . Comparison of energy fluence of picosecond versus Q-switched Nd:YAG laser to treat various pigmentary disorders in Korean patients

IndicationPicosecond Nd:YAG (fluence, J/cm2)Q-switched Nd:YAG (fluence, J/cm2)
Ota’s nevus1,064-nm: 0.65-4.001,064-nm: 2.50 [12]
Melasma1,064-nm: 0.30-0.951,064-nm: 2.60-3.60 [14]
Lentigines532-nm: 0.40-1.50b)532-nm: 0.60b) [17]
1,064-nm: 0.80-0.90-c)
Postinflammatory hyperpigmentation1,064-nm: 0.60-1.501,064-nm: 1.90-2.60 [16]
Café-au-lait macules532-nm: 0.40-0.70b)532-nm: 1.00-1.20b) [18]
1,064-nm: 0.70-2.801,064-nm: 2.60-3.00 [18]
Freckles532-nm: 0.40-0.55b)532-nm: 0.60b) [17]
1,064-nm: 0.55-0.90-c)
Congenital melanocytic nevus1,064-nm: 0.80-6.401,064-nm: 5.00-7.00 [20]
Becker’s nevus1,064-nm: 0.95-1.201,064-nm: 10.00 [23]
Blue nevus532-nm: 0.60b)-c)
1,064-nm: 0.80-6.40694-nma): 5.00-8.50 [25]
Nevus spilus532-nm: 0.40-0.50b)532-nm: 0.50-1.50b) [24]
1,064-nm: 0.70-0.901,064-nm: 3.00-6.00 [24]
Argyria1,064-nm: 0.40-1.001,064-nm: 0.70-8.00 [27]
Melanonychia1,064-nm: 2.00-3.401,064-nm: 7.00 [26]

Nd:YAG, neodymium-doped:yttrium aluminum garnet.

a)This result was a case report treated with a Q-switched 694-nm ruby laser.

b)Results of 532-nm picosecond Nd:YAG laser in the treatment of benign pigmented lesions.

c)Blanks in the table indicate that the energy fluence could not be stated because no cases were reported in the literature review.



Clinical efficacy assessment using a 5-point GAS

Among 48 patients, 45 (93.8%) experienced a clinical response (1%-100% lesion clearance). Thirty-nine patients (81.3%) experienced clinical improvement greater than 25% clearance in their lesions; 16 patients (33.3%) had more than 50% improvement. Clinical improvements, classified according to pigmented disorders, assessed by the GAS are shown in Fig. 1. Most pigmented disorders showed fair to good improvement, except melasma and CMN. Patients with CALM showed the best improvement (GAS, 3.80 ± 0.76) (Fig. 2). Patients with melanonychia showed the second best improvement (GAS, 3.75 ± 1.77) (Fig. 3), followed by lentigines, PIH, and freckles. Notably, a patient with lentigines, whose lesions got worse after the one treatment with QSNY laser, showed an excellent response after two treatments with the PSNY laser (GAS 5) (Fig. 4). Also, patients with Ota’s nevus, whose lesions were refractory to the QSNY laser, showed a good response to the PSNY laser (GAS 4) (Fig. 5). In contrast, two patients with CMN and the patient with blue nevus showed the least improvement, all of whom experienced worsening of their lesions (GAS 1).

Figure 1. Clinical improvement assessed by the Global Assessment Scale (GAS). PIH, postinflammatory hyperpigmentation; CMN, congenital melanocytic nevus.

Figure 2. Clinical images of a café-au-lait macule on the left upper eyelid of a 13-year-old male (A) before treatment and (B) after laser treatments (one session of 532-nm, 0.4 J/cm2, 3-mm, 2 Hz, followed by five sessions of 1,064-nm, 0.7-0.8 J/cm2, 8-mm, 10 Hz); Global Assessment Scale 5.

Figure 3. Clinical images of melanonychia on the left thumb nail of a 20-year-old male (A) before treatment and (B) after five treatments (1,064-nm, 2.0-3.0 J/cm2, 5-6-mm, 5 Hz); Global Assessment Scale 5.

Figure 4. Clinical images of lentigines on the left temple of a 39-year-old female (A) before treatment and (B) after two treatments (532-nm, 0.85-0.90 J/cm2, 2.3-mm, 2 Hz); Global Assessment Scale 5.

Figure 5. Clinical images of Ota’s nevus on the right cheek of a 66-year-old female (A) before treatment and (B) after five treatments (1,064-nm, 1.1-4.2 J/cm2, 4.0-7.4-mm, 10 Hz); Global Assessment Scale 4.

Clinical responses based on the site of involvement showed no significant difference. Facial lesions showed fair to good improvement (GAS, 3.2 ± 1.0), and body lesions showed a similar degree of improvement (GAS, 3.3 ± 1.5).

Adverse events

Some patients experienced transient complications such as erythema, petechia, purpura, and crust formation. All improved spontaneously within a week. There were no persistent adverse events such as scarring or hyper- and hypopigmentation after PSNY treatment.

DISCUSSION

Following the introduction of the concept of selective photothermolysis, laser treatment has been developed to treat various skin discolorations. However, it is common for laser treatment of cutaneous pigmented lesions in Asian patients to cause worsening of the pigmentation. The QSNY laser is known to be an effective and safe treatment for pigmented disorders, although there is a likelihood of recurrence in Asian populations, with side effects such as PIH and mottled hypopigmentation [8-10].

Since the introduction of PSLs, many clinical studies have shown better results in the removal of tattoos and treatment of various pigmented diseases compared to NSLs [2-7,11]. PSLs treat discolorations based on the same principle as NSLs, but with a pulse width one thousand times shorter. This produces an extremely high peak power with the same energy, thus enabling reduction of the photothermal effect while increasing the photomechanical effect (photo-osmosis) [3]. This results in significantly smaller pigment particles that are more quickly removed by macrophages, coupled with less heat transfer to the surrounding tissue. Therefore, the total duration and number of sessions can be shortened in the treatment of pigmented disorders and use of the PSL can therefore reduce adverse events such as PIH [5,6].

In our previous study, we evaluated Korean patients (Fitzpatrick skin type IV) with Ota’s nevus treated with a nanosecond-domain QSNY laser. Moderate improvement (26%-50%) was reported after 4.1 ± 2.0 treatment sessions at a wavelength of 1,064-nm, 2.5 J/cm2, 5-10 nanoseconds, 7-8 mm spot size, and 10 Hz frequency [12]. In the present study, fair improvement (25%-49%) was observed after 3.70 ± 2.16 sessions with the PSNY laser with a mean fluence of 2.45 ± 1.14 J/cm2 (1,064-nm, 0.65-4.00 J/cm2, 5-9 mm spot size, 5-10 Hz). Thus, fewer treatment sessions were required for the PSNY laser compared to the QSNY laser to achieve a similar clinical improvement.

The treatment of melasma is challenging due to its refractory and recurrent nature, especially in Asian skin types. Based on the theory of selective photothermolysis proposed by Anderson and Parrish [13], QS laser treatment such as QSNY, QS alexandrite, and QS ruby has been widely used for treating melasma with variable degrees of success [9]. Recently, the low-fluence, large-spot size application of the nanosecond-domain 1,064-nm QSNY, called laser toning, has been widely used for the treatment of melasma in Asian skin [10]. However, the recurrence rate is high, and rebound hyperpigmentation and mottled hypopigmentation are common side effects. Moreover, many treatment sessions are required. According to a previous clinical study, moderate (25%-50%) clearance of melasma lesions was observed after three to four QSNY laser treatment sessions. The parameters used were a spot size of 8.5 mm in diameter, a fluence of 2.6-3.6 J/cm2, and a repeated frequency of 2 Hz [14].

Meanwhile, in the present study, the laser parameters we used were as follows: 1,064-nm, 0.30-0.95 J/cm2, 8-10 mm spot size, and 10 Hz. We performed multiple passes until mild erythema appeared. The number of treatment sessions was similar to the previous study (3.44 ± 2.55); however, improvement of melasma lesions did not reach 25%-49% clearance on the GAS (2.67 ± 0.80). However, the conclusion that the effect of PSNY on melasma is poor might be premature because there was only a short follow-up period, and more treatment sessions could potentially lead to favorable outcomes. In fact, the recently published our prospective, randomized, split-face, controlled trial comparing two treatments with combined 7 week 2% hydroquinone (daily) and 5 week PSNY (weekly) versus 7 week 2% hydroquinone measured two primary outcomes including relative lightness values (RL*I) and modified melasma severity score (mMASI). The success rate according to RL*I at 1 week after the last procedure of the 2% HQ cream and PSNY laser (test group) was 76.92%, and 2% HQ cream alone (control group) was 2.56%, respectively. Moreover, mMASI showed that the test group achieved better results at 1 week after the last treatment compared to the control group. However, in the previous study, the statistical significance of PSNY laser in the treatment of melasma was not retained during the 18 weeks follow-up period. Absolutely, melasma treatment in Korean skin was confirmed to be intractable even with the PSNY laser [15].

Cho et al. [16] treated Korean patients with PIH using a NSL; a QSNY laser was used for five sessions (1,064-nm, 1.9-2.6 J/cm2, 5-10 nanoseconds, 6 mm spot size, 2-3 passes), and clinical improvements were observed. In our study, fair (25%-49%) to good (50%-74%) improvement was observed after an average of 6.6 sessions of PSNY laser (1,064-nm, 0.6-1.5 J/cm2, 6-8 mm spot size, 1-10 Hz, 2-3 passes). Thus, compared to NSL, lower energy fluence was needed to achieve clinical improvement with the PSNY laser.

Ho et al. [17] showed a moderate to marked improvement in 60% of Asian patients with freckles and lentigines after an average of 1.8 sessions with a QSNY laser (532-nm, 0.6 J/cm2, 5-10 nanoseconds, 2 mm spot size, 5-10 Hz); 10% of the patients experienced PIH. In our study, fair (25%-49%) to good (50%-74%) improvement after 2 sessions with the PSNY laser was observed on the GAS (3.69 for lentigines and 3.17 for freckles), and no significant PIH was observed. A summary of the laser parameters used for treatment is 532-nm, 0.4-1.5 J/cm2, 2.3-4.3 mm spot size, 2-5 Hz and 1,064-nm, 0.8-0.9 J/cm2, 8 mm spot size, and 10 Hz for lentigines; 532-nm, 0.40-0.55 J/cm2, 3.3 mm spot size, 2 Hz and 1,064-nm, 0.55-0.90 J/cm2, 8 mm spot size, and 10 Hz for freckles. Fewer side effects were detected in the PSNY-treated group than the QSNY-treated group.

In the present study, the condition that was treated most effectively with the PSNY laser was CALM. Five patients were treated with an average of 3.00 ± 1.87 treatment sessions. Five patients underwent five sessions of 532-nm laser treatment and three sessions of 1,064-nm laser treatments and showed the best improvement on the GAS (3.80 ± 0.76). In a study by Kim et al. [18], 74.4% of CALM lesions showed clinical improvement of >50% clearance with a 1,064-nm QSNY laser treatment. They performed a split-lesion study using 532-nm and 1,064-nm QSNY lasers; there was a more favorable response and less recurrence in the low-fluence 1,064-nm group compared to the 532-nm treatment group. However, unlike the total of six treatments in the previous study, our study involved an average of three treatments, and we found that the treatment was effectively performed with much lower fluence (QSNY, 2.6-3.0 J/cm2 vs. PSNY, 1.10 ± 0.76 J/cm2).

A variety of lasers is currently used in the treatment of CMN, and QS or normal-mode ruby lasers can be considered alternative treatment options for surgical excision [19]. Combination therapy with a carbon dioxide laser and/or a frequency-doubled QSNY laser showed clinical improvement and aesthetically satisfactory results. However, treatment with the QSNY laser alone showed unsatisfactory improvement [20,21]. Also, in a comparison study between QS ruby and 1,064-nm QSNY lasers, the latter showed inferior efficacy and removed only the superficial components of the CMN [22]. Like the nanosecond-domain QSNY laser, the PSNY laser showed unsatisfactory clearance in the present study. Congenital melanocytic nests exist in the epidermis and/or dermis and are more likely to extend into the deep subcutaneous layer and periadnexal structures. Even though the PSNY laser effectively treats the epidermis and superficial dermis, it does not effectively photothermolyse deeper portions of the nevomelanocytes.

In the present study, treatment of BN led to good clinical improvement (GAS 4), and treatment of a nevus spilus led to excellent improvement (GAS 5). Trelles et al. [23] reported that, among 11 patients who had BN, three showed 1%-25% improvement, five showed 26%-50% improvement, and only one showed 51%-99% improvement after three sessions with the QSNY laser (1,064-nm, 10 J/cm2, 10 nanoseconds, 3 mm spot size, 10% overlap). In our study, a patient with a BN showed 50%-74% lesion clearance after two sessions with a PSNY laser (1,064-nm, 0.95-1.20 J/cm2, 8 mm spot size, 10 Hz, 2 passes). Thus, compared to the QSNY, treatment with the PSNY laser was just as effective with much lower fluence and fewer treatment sessions. Kar and Gupta [24] reported that, among 15 patients with nevus spilus, four showed 25%-50% improvement, six reported 50%-75% improvement, three showed more than 75% improvement, and two reported worsening after an average of 8.7 treatment sessions (532-nm, 0.5-1.5 J/cm2, 3 mm spot size, 2 passes and 1,064-nm, 3-6 J/cm2, 4 mm spot size, 2 passes). In our study, a patient with nevus spilus showed 75%-100% lesion clearance after five treatment sessions (532-nm, 0.4-0.5 J/cm2, 3.3 mm spot size, 2 Hz, 1 pass and 1,064-nm, 0.7-0.9 J/cm2, 8 mm spot size, 10 Hz, 2 passes). Thus, treatment with PSNY showed better clinical improvement with much lower fluence and fewer treatment sessions compared to the QSNY laser.

On the other hand, a patient with blue nevus showed worsening after the PSNY laser treatment. Milgraum et al. [25] reported two cases of blue nevus treated with QS ruby laser, and the lesions were totally cleared after two and three sessions, respectively. Histologic examination of blue nevus often shows a population of heavily pigmented, dendritic spindled cells in the deep reticular dermis, with heavily pigmented melanophages. Treatment targets of the Nd:YAG laser are generally epidermal and superficial dermal lesions. The PSNY laser might not have been able to adequately penetrate the dermis to treat the blue nevus lesion.

Kim et al. [26] treated Korean patients with melanonychia with a QSNY laser. Clinical improvement (25%-50% to 50%-75%) was reported after an average of 2.7 sessions (1,064-nm, 7.0 J/cm2, 9 nanoseconds, 4 mm spot size, 2 passes). In this study, fair (25%-49%) to good (50%-74%) improvement (GAS, 3.75 ± 1.77) was observed after 2.5 sessions with a PSNY laser (1,064-nm, 2.0-3.4 J/cm2, 4-6 mm spot size, 2 passes). Thus, fewer treatment sessions and much lower fluence were needed in the PSNY laser-treated patients for a similar clinical outcome.

During the study period, there were no persistent or serious adverse events associated with laser therapy.

Overall, compared with the laser settings (especially in energy fluence) resulted in previous studies [12,14,16-18,20,23-27], much lower energy fluence was applied in our patients (Table 3). However, due to the limitations of the retrospective methodology used in our analysis and the lack of device standardization, accurate comparison is challenging.

Our study has several drawbacks. First, the number of study subjects was not enough to show the statistical significance in presenting the effectiveness as a recommendable therapy. Thus, although our findings suggest the potential treatment option for intractable pigmentary disorders, our therapy should not be recognized as a recommendable treatment. Our results were based on preliminary study, and further randomized, controlled study should be conducted for more patients. Second, our study was performed on the basis of retrospective nature. Thus, our study is not so precise as a prospective clinical trials in controlling confounding factor and bias. Third, since control group was lack in the study, we could not directly compare the effect of our therapy with that of different method. Fourth, the study was performed in single center. The effect of treatment largely depend on the skill and experience of physician. Thus, it is concerned that the outcome of therapy may be diversely manifested among centers. Despite these limitations, we believe that the results of this preliminary study can be a therapeutic reference for the refractory pigmented disorders in Asian skin.

In conclusion, the clinical efficacy of a 750 PSNY laser device was demonstrated in the management of a selection of pigmented lesions, comprising nearly all the pigmentary disorders encountered in Korean skin. The PSNY laser used in this study generated a smaller photothermal effect during the removal of pigment compared to current laser treatments, required less time, and was associated with minimal adverse events. This device offers a new and potentially safe therapeutic modality for various pigmented lesions in Asian patients. A novel PSNY laser is especially promising to treat refractory lesions that require long treatment periods with the conventional QSNY laser.

ACKNOWLEDGMENTS

None.

AUTHOR CONTRIBUTIONS

Conceptualization: YJC. Data curation: SJB. Formal analysis: SJB, WSK. Investigation: WSK, YJC. Methodology: WSK, YJC. Project administration: YJC. Software: SJB. Validation: YJC. Visualization: YJC. Supervision: YJC. Writing–original draft: SJB, WSK, YJC. Writing–review & editing: all authors.

CONFLICT OF INTEREST

Drs Won-Serk Kim and Young-Jun Choi works as a consultant for Lutronic Corporation. The company had no role in the design and conduct of the study, analysis or interpretation of the data, and manuscript publication. Young-Jun Choi is the Editor-in-Chief of the journal, but was not involved in the review process of this article. Otherwise, there is no conflict of interest to declare.

FUNDING

None.

DATA AVAILABILITY

Contact the corresponding author for data availability.

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