Dermatologists are very often consulted for benign epidermal pigmented lesions (EPLs), which are optimally treated by selective removal of the target pigment [1,2], achieved first with shorter visible lasers with the highest absorption coefficients in melanin achieving photothermal destruction of the excess melanin pigmentation. The early continuous wave versions of these lasers were, however, associated with excessive epidermal damage [3-5]. Anderson and Parrish [6]’s theory of selective photothermolysis (SPT) in 1983 offered selective pigment removal, requiring high peak powers, an appropriate wavelength, and an exposure time shorter than the thermal relaxation time of the tissue surrounding the target pigment [7]. This led to the nanosecond-domain Q-switched neodymium-doped yttrium aluminum garnet (Q-Nd:YAG) laser with a main wavelength of 1,064 nm that could be frequency doubled to produce 532 nm, and the Q-switched 532 nm wavelength became the treatment of choice for EPLs [8]. Overtreatment can cause damage to the dermoepidermal junction resulting in inflammation, and particularly in darker Asian skin types, this can lead to the formation of postinflammatory hyperpigmentation (PIH) in the epidermis or dermis [9]. The written informed consents were obtained from all patients for the publication of this case report.

A new generation of Q-Nd:YAG has become commercially available (HOLLYWOOD SPECTRA^TM; Lutronic Corporation). Amongst system innovations is the extension of the quick pulse-to-pulse (dual-pulse) mode to include a quadruple-pulse (Q4) mode with a macropulse of 150 µs comprising 4 ns-domain sub pulses. Seven Korean subjects with EPLs participated in the study, 5 females and 2 males, ages from 29 to 62 years (mean 48.43 ± 10.47 years) with Fitzpatrick skin types (FSTs) III and IV. Table 1 shows the patient demographics. Topical anesthesia (lidocaine 9.6% under occlusion technique, 30-50 minutes) was applied. Subjects were treated with the 1,064 nm Q-Nd: YAG in Q4 mode with the zoom handpiece using a 2 mm spot “painted” over the target lesions with the aim of avoiding too much overlap. Macropulse fluences ranged from 26-40 J/cm² depending on the lesions being treated, and the repetition rate was 10 Hz (Supplementary Video 1). The desired endpoint was a grayish color change or frosting without immediate separation of the epidermis from the dermis, and a mild hydrocortisone cream was applied as post-treatment care. Two to 4 sessions were given, 2-3 weeks apart with a follow-up of 3-4 weeks after the final session.

Table 1 . Patient demographics, pain score, GAIS score and patient satisfaction rating

Patient no.	Sex/age (yr)	FST	Pain level (VAS, 0-10)	GAIS score	Patient satisfactiona)
1	F/54	FST III	4	4	++
2	M/56	FST IV	3	4	+++
3	F/43	FST IV	3	4	+++
4	F/52	FST IV	3	4	+++
5	M/43	FST III	3	4	+++
6	F/62	FST IV	4	4	++
7	F/29	FST III	3	4	+++

GAIS, Global Aesthetic Improvement Scale (quintile scale, 0-4); FST, Fitzpatrick skin type; VAS, visual analogue scale (zero: no pain; 10: worst possible pain).

^a)“–” = dissatisfied (0%-25% improvement); “+” = somewhat satisfied (26%-50%); “++” = satisfied (51%-75%); “+++” = very satisfied (76%-100%).

Digital clinical photography of both sides of the face was captured at baseline, before each treatment session and at the final assessment, 3-4 weeks after the final treatment session (Mark-vu^® Digital Image Analysis System; Pure Tone Aesthetics). Based on the clinical photography, scoring on a Global Aesthetic Improvement Scale (GAIS) was performed by two independent blinded dermatologists using a quintile scale (scores from 0-4). At the final assessment, patients were shown the clinical photography of their lesions at baseline and were asked to score their satisfaction with improvement of the lesions as follows: “–” = dissatisfied (0%-25% improvement); “+” = somewhat satisfied (26%-50%); “++” = satisfied (51%-75%); and “+++” = very satisfied (76%-100%). Pain during treatment was scored on an 11 point visual analogue scale where zero represented no pain and 10 represented the worst possible pain.

All seven patients completed the trial. Very good to excellent clearance of the target lesions was seen in all seven subjects at the final follow-up assessment. In the GAIS, all patients achieved the score of 4 (Table 1). Apart from the expected mild erythema, no adverse events were noted during or after treatment, and the degree of pain was reasonable, with 5 subjects scoring 3 and 2 subjects scoring 4 out of 10 (Table 1). Subjective patient satisfaction was high, with all patients rating their improvement as over 50%, and 5 out of 7 scoring over 75% improvement (Table 1).

Clinical photography from two representative cases is shown in Figs. 1, 2. In Fig. 1, a 54-year-old-female with FST III is shown at baseline and at follow-up (patient no. 1). Fig. 1A shows the findings at baseline, with multiple small discrete pigmented lesions on both sides of the face especially over the cheeks and nose. She had 4 treatment sessions 3 weeks apart with doses ranging from 25 to 30 J/cm². Fig. 1B shows the good result at 3 weeks after the fourth and final treatment. A 56-year-old male is seen at baseline in Fig. 2A, with multiple senile lentigines (patient no. 2). He received four treatment sessions, three weeks apart at doses ranging from 26 to 36 J/cm², and the good result at three weeks after the fourth and final treatment is seen in Fig. 2B. The treatment endpoint was a grey change/frosting over the target lesion with no immediate peripheral erythema.

Figure 1. A 54-year-old female (patient no. 1) with (A) epidermal pigmented lesions at baseline and (B) 3 weeks after the 4th and final treatment.

Figure 2. A 56-year-old male (patient no. 2) is seen at baseline in (A), with multiple senile lentigines and at (B) 3 weeks after the 4th and final treatment.

There are limitations in this case report, namely the small number of participants as a major limitation limiting the ability of the results of the study to be extrapolated into the general population. However, the optimistic result seen in all subjects with no unwanted side effects warrant further prospective controlled studies with larger populations, and split-face comparative studies with 532 nm would add to acceptance of the Q-Nd:YAG Q4 approach. A second potential limitation is the comparatively short follow-up, but it was still sufficient to assess the potential for PIH formation which did not occur in any patient.

Although treatment with the 532 nm wavelength is the usual choice for discreet epidermal lesions, there is a very narrow safety margin because of the high absorption in melanin, and inflammation generated at the dermoepidermal junction can easily lead to epidermal and/or dermal PIH in darker-skinned Asian patients. The wavelength of 1,064 nm has a much lower absorption coefficient in melanin, but sufficient irradiances, such as those delivered by the 1,064 nm Q-Nd:YAG, can have an excellent effect in selective pigment eradication with appropriate parameters. The laser toning technique was developed around a decade ago for the treatment of melasma using the 1,064 nm wavelength with larger spot sizes and low fluences, based on the concept of subcellular SPT as mentioned earlier and remains a good option for treatment of the diffuse pigment associated with melasma, but has not been so effective for discrete EPLs [10-12].

The author’s new approach embodies laser toning for EPLs with the new generation 1,064 nm Q-Nd:YAG, using the Q4 mode rather than the single mode or the dual-pulse technique which had previously proved effective [13], and employing higher fluences (26-40 J/cm²) over a 2 mm spot size delivered by the focusing zoom handpiece. The system repetition rate is set to 10 Hz, and the distancing piece of the handpiece is held in constant gentle contact with the skin while the handpiece is moved in a dynamic “painting” fashion over the lesioned skin, as distinct to a static “stamping” approach. This process is demonstrated in a short video which is available in the supplemental data, including showing the fluences used in the present case report being selected on the system GUI (graphic user interface, or touch screen) (Supplementary Video 2). It is important to keep the distancing piece in contact with the skin because of the focusing characteristics of the incident beam where the laser focal waist is beneath the skin surface. Moving the handpiece away from the tissue will decrease the spot size, increasing the irradiance in an inverse square ratio, raising the possibility of collateral thermal damage.

The 2 mm spot size was chosen in combination with the higher fluences to increase the irradiance of the laser energy incident on the target EPLs, but at the same time to help to limit the depth of penetration to the epidermis only. The higher the irradiance that can be achieved in W/cm² (to an appropriate level), the more effective is the pigment destruction through a combination of photoacoustic and photothermal effects while the surrounding normal tissue is spared.

The Q4 mode was chosen because of its ability to deliver the appropriate energy in a gentler fashion than the single pulse mode. Each of the nanosecond-domain subpulses is capable of some photoacoustic effect together with a photothermal effect, and the train of four subpulses in the 150 µs macropulse can efficiently achieve the desired endpoint of the grayish colour change or frosting through quick repetition and in particular the accumulation of the photothermal effect within the excess levels of pigment particles. The multipulse approach enhances the photothermal effect through the train of multipulses in each macropulse. The grayish color change or the appearance of frosting indicates that damage has been well-limited to the excessive epidermal melanin particles. In conclusion, the author’s approach with high fluences and small spot size in combination with the 1,064 nm Q-Nd:YAG Q4 mode proved safe and effective in the clearance of EPLs with bearable pain and a short downtime. There were no unexpected adverse events, and patient satisfaction was high. Despite the small patient population, the very optimistic results seen in this small case series certainly warrant further study with a controlled approach and a much larger patient population.

Supplementary materials can be found via https://doi.org/10.25289/ML.24.029.

I thank Dr. R. Glen Calderhead for his review and revision of this manuscript.

All work was done by JKH.

No potential conflict of interest relevant to this article was reported.

None.

Contact the corresponding author for data availability.