Laser therapy of giant congenital melanocytic nevi

ARTICLE

Melanocytic nevi are common, but giant congenital melanocytic nevi (GCMN) are present in 1/300,000 to 1/500,000 new-born (for 750,000 new-born/year in France, 10 new cases/year in France) [1]. Congenital nevi are divided into small congenital nevi < 20 cm² in diameter which have a low reported lifetime risk of developing melanoma; and GCMN >20 cm² in diameter which have a reported lifetime risk of 5 % to 10 % of developing melanoma [2]. Most agree upon the need for early treatment of GCMN [3]. GCMN contain a large quantity of melanin and to improve the quality of life of the patients by erasing the disfiguring superficial lesions that are present since birth, treatment must be carried out. The smaller lesions can be easily eliminated surgically, because histological examination of the tissue may reveal cellular atypia [3-5]. The surgeon must seek to minimize the risk of malignancy. Various therapeutic approaches, such as surgical excision, dermabrasion, curettage, cryosurgery, electrosurgery have been used in treating GCMN. All these methods produce postoperative scarring. The objective calls for radical excision of all pigmented areas; this may impossible because of the risk of leaving the patient with disfiguring scars [3] or alterations in skin texture with curettage [4, 5]. The problem is that congenital melanocytic nevi may have nevomelanocytes around and within hair follicles, exocrine ducts, vessels walls, and the perineurium of cutaneous nerves [1]. Further distribution of nevomelanocytes can be seen surrounding these structures as well as around collagen bundles in the lower portions of the reticular dermis and subcutis. Some GCMN can be difficult to excise in totality, since nevomelanocytes may also occur in subcutaneous fat, fascia, and even muscle. So no surgeon can be sure that removal can be achieved with good lateral and subcutaneous margin [3]. This explains the number of recurrences, which is also possibly because of the tendency of involvement of GCMN in young children [6].

The use of laser in the treatment of GCMN is controversial. Some feel that lasers can reduce the melanocytic mass and the risk of malignancy, but others are more concerned about the potential increase in the risk of sub-lethal laser damage [7]. The aim of this review was to access treatment of GCMN with laser as an alternative to surgery [8-12]. Laser is a surface technique proposed when surgical excision cannot be performed because the surface is too large or the localization is incompatible with surgery.

In the past, continuous wave lasers, such as the argon (wavelength, lambda  = 488nm) (13), carbon dioxide (wavelength, lambda  = 10,600nm) [14, 15], and normal mode ruby laser (wavelenght, lambda  = 694nm) [13] have been used to ablate nevomelanocytic lesions, including congenital nevi. Nowadays ultrashort high energy pulsed CO₂ laser [8, 9,
12] and the normal mode ruby laser [16, 18] are the two lasers available.

Water-absorbed laser

Laser CO_2:

The carbon dioxide laser emits light at lambda  = 10,600nm (wavelength). This long infrared wavelength is strongly absorbed by water, which is the main component of skin. The laser light is absorbed within 20 m m of tissue. But with the conventional carbon dioxide laser, the surrounding tissue is heated up through heat conduction away from the impact site. In general, continuous wave carbon dioxide laser ablation causes greater scarring than a well executed surgical excision for GCMN, and occasionally pseudomelanoma may result [6, 14, 15]. The carbon dioxide lasers have been limited by the tendency of the laser to leave behind a zone of coagulation necrosis around the treatment site, which measures up to 1 mm across [12]. This often results in unacceptable scarring. To confine the damage to the impact site, the laser energy must be delivered in a time short enough that thermal conduction away from the impact is minimal. The desirable zone of thermal damage is 50 to 100 m m. This is small enough to successfully seal small dermal blood vessels, to maintain a bloodless field. To confine the thermal energy, a pulse duration of approximately 1 msec is necessary, and enough energy is to be delivered to completely vaporise the water in the target tissue. The emergence of the new generation of ultrashort high energy pulsed CO₂ lasers give us the capability for removing pigmented lesions with less risk of scarring [8-11]. Kay first reported successful treatment of giant congenital melanocytic nevus with the high energy pulsed CO₂ laser [9]. The high energy pulsed CO₂ laser has been used in 9 newborns and 5 children from 5 to 15 years old [12]. In all patients, the pulsed power was of 15 watts and a pulse duration of 0.45 seconds, mode pulsed, 2 to 3 passages. For each region of the nevi, two passages were realised in the same session. Between the two passes, the resulting desiccated tissue debris was wiped away with dry gauze saline soaked. Additional passes are carried out over the remaining lesion to smooth it out, but with increasing risk of complications. The treatment was undertaken with local anaesthesia with Emla® cream, and Xylocaïne® in the 5 children. The 9 new-borns needed general anaesthesia and a one week to one month’s hospitalisation for the largest GCN. The first cases had a curettage of the majority of the lesions [4, 5], and laser on the periphery of GCN that you can not treat with curettage. Seven patients only received laser therapy. The treatment with the high energy pulsed CO₂ laser achieved 70 to 90 % clearing of the giant nevi in 9 to 14 children (Figure 1a,b). One child developed a hypertrophic scar on a companion nevi, and another on the GCN. Even with high energy pulsed CO₂ laser we still produced a relevant amount of heat injury along with an immediate dermal shrinkage and consecutive fibrosis after wound healing. One child required a graft skin because of tissue necrosis, in relation with an intravascular coagulation and septic shock. The mean follow up was 3 years without any case of cutaneous melanoma. One child died from an intracerebral tumor. She had a very large GCN on the neck, shoulders, and back. In comparison with curettage, the quality of the skin, and its suppleness was better with CO₂ laser [4, 5].

There are several advantages in this technique. Treatment can be realized for any size of nevus. Precocity of treatment, in the first fifteen days, is not required for the quality of the esthetic outcome, in comparison with early curettage of giant congenital nevus in children. In the older child in the case of medium or large size nevus the initial results (6 to 12 months) seem to be good, but longer follow ups have seen a low rate of improvement. High energy pulsed CO₂ laser provides satisfactory cosmetic results, with short cicatrisation time. Thermal damage is limited. It allows the treatment of the companion nevi at the same time. Bleeding is minimal in comparison with the other surface techniques: curettage [4, 5] and dermabrasion [1, 3]. The risk of malignant transformation should be greatly reduced (because of the reduction rate of HMB₄₅ melanocyte) although not totally [2]. This treatment can be repeated.

The disadvantages are the complication of laser CO₂ treatment in the newborn (pain, scarring, secondary infection); the high cost of the equipment in comparison with curettage [4, 5]; the recurrence of the deeper lesions (specially in the older child, who had a migration of the nevomelanocyte as far as the hypodermis) [8-12]. We do not have good efficiency for the child aged from 5 to 15 years old (Figure 2a,b,c). This child had, after initial laser destruction of congenital nevi, a repopulation of the initially depleted layers in 6 months. Due to the physical properties of CO₂ laser, the deepest parts of a compound nevus will not be treated in a manner that results in all dermal nests being removed [15].

Erbium (Er:YAG) Laser: lambda  = 2940nm (wavelength)

Er:YAG laser corresponding to a 3000nm water absorption peak, is 15 times more efficiently absorbed than the CO₂ laser. Tissue is ejected in the form of small particles by mechanical forces. There is no hypopigmentation using this laser instead of CO₂ laser [12]. There should be an increase in hemorrhagic risk when Er:YAG is used for the neonate, just like with dermabrasion [5].

CO₂ (lambda  = 10,600nm)/Er:YAG (lambda  = 2940nm) Laser: DermaK®

To achieve haemostasis comparable to the CO₂ laser, and still have a pure ablative mode, one laser has combined an ablative Er:YAG laser with a vaporizing pulsed CO₂ laser. It seems to be one of the most interesting lasers for the treatment of GCMN in the neonate [8-12], with less risk of neocollagenesis (in comparison with the CO₂ laser, and so diminishing the risk of hypertrophic scar), and of bleeding (unlike the Er:YAG). But there is no published data for the moment [1]. Combined treatment has been proposed by Cisnerios and Del Rio in oral communications but no results are available [19]. The combined treatment begins with laserablation using the erbium Derma K® laser (wavelength 2940nm; repetition rate 7-8 Hz; spot size 3-4mm; fluence 1.7 to 2J/cm²; pulse duration 350ms), associated to CO₂ laser (simultaneous emission of 2 to 5 W). Generally 3 to 5 passes are necessary, according to the width of the lesion. In a second step the treatment focusing on depigmentation proceeds using the Nd:YAG Q-switched laser 532nm or 1064nm wavelength, and/or intense pulsed light with wide band (515-1200nm). Biopsies are done before treatment, but there is no control after the session, and no follow-up. In the case of GCMN, the author recommended beginning the treatment as soon as possible, because the lesions are thinner.

Pigment-specific laser

Mechanism

The introduction of short pulsed laser: the Q-switched ruby laser, the Q-switched neodynium:YAG laser, the Q-switched alexandrite laser has made it possible to treat various pigmented skin lesions. The Q-switched ruby laser lightens, and may clear pigmentation from the nevus of Ota [20], as well as small to medium size nevi [21, 23]. Congenital nevi contain deep dermal pigment mostly in nevomelanocytes, so mostly it is the Q-switched ruby laser which has been used for the relatively deep penetrating ruby laser photons. Q-switched lasers exert their biological effect by selectively targeting melanosomes in melanocytes and keratinocytes [24]. Based on the selective photothermolysis of melanosomes, the high local temperature changes induced by laser irradiation allows the destruction of melanocytic cells by laser therapy. These require high absorption in melanin, and deep penetration. The Q-switched laser has a device to store the energy in the laser before releasing it in nanoseconds. The enormous but brief fluence limits the non specific thermal damage and the subsequent scarring in the skin. The shock wave is instantaneously caused by the generation of temperatures superior to 1000 °C, that occur, and the subsequent abrupt thermal expansion [25]. Organelle-specific damage occurs as a result of the selective absorption of high energy [24]. Laser light produces a rapid shock wave. It seems likely that the mechanism for pigment removal would include direct ejection as evidenced by lens spatter, combustion of particles (shown by gas bubbles visible histologically) [26], and direct fragmentation of particles (again visible microscopically) and highlighted by translocation of pigment. There is a reduction in pigment particle sizes leading to melanosome fracture [24]. Melanosomes are destroyed as a result of both the thermal and photoacoustic effects of the laser energy [27]. Melanocytes lethality correlates with melanosome fragmentation, and with high pressure acoustic waves [24]. This combination underlies the biological effects.

Available lasers (Table I) include green light pulsed lasers such as the pigmented lesion: pulsed dye laser (wavelength lambda  = 510nm, 300nsec) [28, 29] and the frequency-doubled Q-switched Nd:YAG laser (wavelength lambda  = 532nm, 5-10nsec) [7]. As green light is absorbed to a high degree in melanin but penetrates just superficially into the skin, these lasers can only be used for the treatment of pigmented epidermal lesions. Red light pulsed lasers include the Q-switched ruby laser (wavelenfth, lambda  = 694nm, 20-50nsec) [21, 23, 30], the Q-switched Alexandrite laser (wavelength, lambda  = 755nm, 5-100nsec) [29], the normal mode ruby laser (wavelength lambda  = 694nm, 300-3000m sec) [16-18], and the normal mode Alexandrite laser (wavelength, lambda  = 755nm, 2-20m sec). Infrared pulsed lasers such as the Q-switched Nd:YAG laser have a wave length of lambda  = 1064nm and a pulse duration of about 10nsec [23]. They have a low absorption by melanin, but deeper penetrating potential through the skin, and therefore might be even more suitable for treating deep dermal pigmented lesions.

Since melanin absorption decreases with increasing wave length, the highest absorption is caused by green light pulsed lasers, the lowest by infrared lasers [7]. On the other hand as penetration depth intensifies when the wave length increases, infrared lasers may be used for the treatment of thicker lesions. The normal mode ruby laser is of much longer duration and high energy fluences could target the nest of cells [16-18, 20]. In GCMN, the pigmented cells are clustered in relatively large nests that also contain cells with little pigment. The submicrosecond pulses of the Q-switched ruby laser target the individual pigmented cells [24]. Therefore, the poor clinical response of this laser may be the result of a failure to destroy all the cells in the nests [20].

Clinical studies (Table II)

In recent years, many studies about laser treatment of melanocytic nevi and congenital melanocytic nevi have been published. Most studies reported beneficial effect of laser therapy, with lightening or clinical removal of the lesion [31, 32]. However, with Q-switched ruby laser partial effectiveness and recurrence even after multiple treatments were reported [22, 29]. The use of longer pulse ruby lasers (pulse duration, 0.5-3 milliseconds) show that they offer advantages over the Q-switched laser, by enhancing the penetration of 694nm laser light, thus ensuring complete destruction [17,30]. Normal mode ruby laser is the most used (pulse duration:0.3-1.10^-3 sec, energy fluence: 10-30J/cm2, spot size:10 ´  10mm or 15 ´  15mm, at intervals of 1 to 4 months) [16]. But for the patients who had a large area of skin to be treated, or who are young, intubation and general anaesthesia is necessary. The pigmented lesions were significantly reduced almost to the level of the surrounding normal skin after 4 laser treatments. The treated regions became epithelialized 2 weeks after laser treatment and residual pigment became gradually apparent thereafter. Repigmentation did not occur after 6 weeks, and the appearance of the treated regions stabilised. The treated areas were virtually free of scarring, and the skin texture resembled that of the surrounding normal skin [16-18, 33]. The normal mode ruby laser is effective in treating congenital nevi. In the superficial and deep portions of GCMN, a number of nevomelanocytes can be destroyed [18, 20]. Thus decreasing the number of cells potentially capable of malignant transformation ?

Duke et al [17] have treated 31 nevi but from different origins (benign acquired, atypical, congenital), and with 4 different laser modalities. The entire lesions were excised 4 weeks after the last treatment, so no conclusions can be reached on the efficiency and on the malignancy risk.

Conclusion

The measurement of the depth of laser induced destruction seen after a single treatment appears to be approximately 0.2 mm for the Q-switched Nd:YAG laser, and 0.4 mm for the Q-switched ruby laser, when measured from the top of the papillary dermis [23]. Even repetitive Q-switched laser treatment will not result in the complete eradication of most congenital nevi. However, due to the limited penetration depth of laser therapy of about 0.2 to 0.4mm, none of the studies described a complete histological removal. In young children some melanocytes have no melanosomes, so are not well treated and reappear. The pulsed dye laser (wavelength, lambda  = 510nm, 300nsec) has contradictory results [28, 29], and the normal mode ruby laser (wavelength, lambda  = 694nm, 300-3000msec) [16-18, 33] seems to be the best laser for this indication, but very few of these apparatus are available in Europe, and there are only a few studies. The combined use of normal mode and Q-switched ruby lasers [17, 33]; or ultrashort high energy pulsed CO₂ laser and Q-switched ruby or Nd:YAG lasers [19], can give us a solution.

Hair removal laser (Table III)

After normal mode ruby laser, unsightly hair growth was also reduced. Destruction involved the hair bulb, where an abundance of melanocytes and melanin pigment are aggregated in a well demarcated pattern. Hair can regenerate to a certain extent after each treatment, but hair growth became less dense and the hairs became thinner as the treatment progressed, this contributed greatly to the cosmetic appearance, and to the texture of the skin [16].

Ten hypertrichotic compound nevi on the face have been treated successfully with both the long pulsed Alexan drite wavelength, lambda  = 755nm and wavelength, lambda  = 800nm diode lasers [34]. The average number of treatments needed to lighten pigmented lesions by at least 75 % was 3 for the alexandrite and 5 for the diode. The nevi responded equally to both lasers. Hair free intervals lengthened after each treatment. All subjects achieved at least a 90 % decrease in hair density with high overall satisfaction in all laser groups. Pre- and post-treatment biopsies from 5 patients showed a pigment decrease, miniaturization of hair follicles, as well as mild fibrosis. No obvious malignant changes were detected in these nevi by simple histologic examination in 12 months follow-up period, which is very short. Intense pulse light (590-1200nm) has also been used [35].

Risks of lasers

The potential deleterious effect of laser exposure is malignant transformation [31, 32]. GCMN have an increased risk for the development of melanoma. It is not known whether nevomelanocytes in these lesions possess a higher intrinsic potential for malignant transformation or whether the increased risk can be attributed to the higher number of nevomelanocytes [1, 2]. A number of naevus cells in the superficial and deep portions of congenital nevi can be destroyed by laser exposure [18]. This decreases the number of cells potentially capable of malignant transformation [23]. In several lesions many of the residual deeper melanocytes appeared to be unaffected, these are the nevomelanocytes with the greater risk of transformation. Moreover, it has been demonstrated that, after initial laser destruction, repopulation of the initially depleted layers will occur in 3 to 6 months with the Q-switched ruby laser [22].

The only long term follow-up study of nevi after laser exposure is from Japan, and reported no histological evidence of malignant changes 8 years after normal ruby laser treatment for congenital nevi [18]. Unlike UV radiation, the effects of lasers on tissue are primarily thermal [7, 25, 32]. Pigmented cells in the epidermis or dermis can be selectively targeted and destroyed by laser light of a specific wavelength and pulse duration. Selective photothermolysis of nevomelanocytes, involve high local temperature transients, leading to melanosome fracture [27]. Thermal and mechanical damage appear to be the main mechanisms of injury caused by the Q-switched lasers (ruby or Nd:YAG) [23]. In contrast, UV irradiation is known for its capability to inflict specific DNA damage [36].

Ultrarapid heating by the Q-switched laser pulse results in rapid heating of the cellular cytoplasm. Non-lethal heating occurs in the cell, an induced heat-dependent production of stress protein [37]. Deleterious long term effects of heat induced changes could increase incidence of squamous cell carcinoma (has been reported in patients with burn scars) [38]. We know that non-coherent near infrared light protects normal human dermal fibroblasts from solar ultraviolet toxicity [36], but we have few studies on nevomelanocytes, and with pulsed laser light [39-43]. Many clinical studies [16] lack skin biopsies to observe the histological changes, or long term follow-up to determine the influence on the risk of development of malignant melanoma after laser irradiation [9, 16, 17, 21, 22]. Treatment with the Q-switched Nd:YAG laser occasionally resulted in focal epidermal necrosis [23], extensive extravasation of erythrocytes (although the endothelium of the capillary tufts within the dermal papillae appeared viable). Numerous dyskeratotic cells were present in the epidermis. A mild neutrophilic and hypereosinophilic infiltrate within the necrotic epidermis and throughout the papillary dermis was identified. Necrotic and occasional multinucleated viable nevomelanocytes were identified in the papillary dermis. An increase of melanophages was observed.

In a previous study in normal skin, melanocytes receiving sublethal laser pulses appeared to be activated [7]. At present GCMN cannot be removed entirely by lasers which follow the principle of selective photothermolysis [18]. In particular, a theoretical risk exits regarding potential activation of GCMN by selective photothermolysis Q-switched Nd:YAG laser [41]. After laser treatment of nevi, in two studies a pseudomelanoma aspect of a nevi has been seen [14, 15], or an atypical clinic aspect (after a hair removal high pulsed diode laser) [44]. Pseudomelanoma is a pigmented lesion that histologically resembles a superficial spreading melanoma, with an atypicality of cells after partial excision and subsequent recurrence [6]. Laser irradiation of nevomelanocytic lesions could induce a neoplastic like change [14, 15]. A partially removed lesion would repigment in a clinically and histologically atypical manner. The biological effects of high fluence laser irradiation on sub-lethal damaged melanocytic cells still remain unclear [41]. Studies of Q-switched laser treatment of melanoma cell lines in vitro showed changes in cell surface receptor expression (integrin), with subsequent alteration of such cellular behavior as migration [42, 43]. A possible increase in the migration of nevomelanocytes induced by laser irradiation could be a mechanism responsible for malignant transformation. Three human melanoma cell lines have been irradiated by a Q-switched Alexandrite laser (wavelength, lambda  = 755nm, 5-100sec) at fluences ranged from 0.85 to 2.2J/cm² [39]. Laser irradiation significantly increases DNA damage leading to an increase in p16 expression. The p16 gene as been proposed as the candidate gene for melanoma. Patients with p16 mutation will have a higher risk of melanoma after sub-lethal laser damage. But it was an in vitro study, without the enzyme capacity of the gene to repair. The cells were irradiated twice a week, which is more frequent than in human use (one time per 2 to 3 months). Thus the biological behavior of melanoma cell lines may not truly reflect that of nevoid melanocytes. These changes at least indicate that the sublethal effect of lasers is more than thermal in nature.

At present, no malignant transformation following Q-switched laser treatment has been reported. Methods to assess potential malignant transformation in laser irradiated GCMN are currently unavailable. However the examination of modulation of cell adhesion molecule changes could reflect functional behavioural changes of nevomelanocytes [42]. A lentigo maligna treated with a ruby laser recurred, and a lentigo melanoma arose in this lentigo [45]. It is unclear if this change was correlated to the laser treatment.

CONCLUSION

The objective of treatment of giant congenital nevi is to obtain ablation without side effects or aesthetic consequencies [1, 3]. But to date such treatment does not exist.
Lasers should only be regarded as a treatment option for GCMN that cannot be surgically excised. Treatment should be carried out largely to improve the quality of life of the patients, by erasing the disfiguring superficial lesions, but can’t improve the risk of melanoma and may increase it. The contribution of lasers to the treatment of congenital nevi may always be discussed. For the moment laser therapy of GCMN should be restricted to well controlled studies, Asian populations [40] or to individual patients in whom surgical procedures are not possible or would result in unacceptable scarring [31, 32]. The hopes that Q-switched laser could give us a better way of treatment, with less pain, and no scars [21-23], have failed. We need an improvement of the technology in this field and hopefully the picosecond systems will be available in the future [41].

This work was presented at the XVIII International Pigment Cell Conference (IPCC), Hotel Zuiderduin, Egmond aan Zee, The Netherlands, 9-13 September 2002.

REFERENCES

1
Michel JL, Chalencon F, Gentil-Perret A, Fond L, Montélimard N, Chalencon V, Cambazard F. Le naevus pigmentaire congénital: pronostic, possibilités thérapeutiques. Arch Pédiatr 1999; 6: 211-7.

2
Benoit-Durafour F., Michel JL, Godard W., Chalencon V., Mazzocchi C., Chalencon F., Cambazard F. Mélanome néonatal sur naevus géant congénital. Ann Dermatol Venereol 1999; 126: 813-6.

3
Lawrence CM. Treatment options for giant congenital naevi. Clin Exp Dermatol 2000; 25: 7-11.

4
Casanova D, Bardot J, Andrac-Meyer L, Magalon G. Early curettage of giant congenital naevus in children. Br J Dermatol 1997; 194: 261-7.

5
Michel JL, Laborde-Milaa Roux V, Chavrier Y, Roux V, Chalencon F, Cambazard F. Curetage néonatal des naevus congénitaux géants. Ann Dermatol Venereol 2000; 127: 23-8.

6
Kornberg R, Ackerman AB. Pseudomelanoma: recurrent melanocytic nevus following partial surgical removal. Arch Dermatol 1975; 111: 1588-90.

7
Anderson R, Margolis R, Watanabe S, Flotte T, Hruza G, Dover J. Selective photothermolysis of cutaneous pigmentation by Q-switched Nd:YAG laser pulses at 1064, 532, and 355 nm. J Invest Dermatol 1989; 93: 28-32.

8
Bekhor PS. The role of pulsed laser in the management of cosmetically significant pigmented lesions. Australas J Dermatol 1995; 36: 221-3.

9
Kay AR, Kenealy J, Mercer NS. Successful treatment of giant congenital melanocytic naevus with the high energy pulsed CO2 laser. Br J Plast Surg 1998; 51: 22-4.

10
Grande Carpo B, Grevelink JM, Virnelli Grevelink S. Laser treatment of pigmented lesions in children. Seminars in Cutaneous Medicine and Surgery 1999; 18: 233-43.

11
Kaufmann R. The role of laser in the treatment of nevocellular nevi. Lasermedizin 2000; 15: 168-73.

12
Michel J-L, Caillet-Chomel L. Traitement par laser CO2 superpulsé des nævus congénitaux géants. Arch Pédiatr 2001; 8: 1185-94.

13
Oshiro T, Maryuyama Y. The ruby and argon lasers in the treatment of naevi. Ann Acad Med Singapore 1983; 12: 388-95.

14
Trau H, Orenstein A, Schewach-Miller M, Tsur H. Pseudomelanoma following laser therapy for congenital nevus. J Dermatol Surg Oncol 1986; 12: 984-6.

15
Dummer R, Kempf W, Burg G. Pseudomelanoma after laser therapy. Dermatology 1998; 197: 71-3.
16
Ueda S., Imayama S. Normal-Mode Ruby Laser for treating congenital nevi. Arch. Dermatol 1997; 133: 355-9.

17
Duke D, Byers R, Sober AJ, Anderson RR, Grevelink JM. Treatment of benign and atypical naevi with the NMRL and the QSRL. Arch Dermatol 1999; 135: 290-296.

18
Imayama S., Ueda S. Long and short term observations of congenital nevi treated with the Normal-Mode Ruby Laser. Arch Dermatol 1999; 135: 1211-8.

19
Cisnerios JL, Del Rio R. Laser treatment of congenital nevus. International Master Courses of Laser Dermatology. Marseille. 2-3 November 2001.

20
Ueda S, Isoda M, Imayama S. Response of naevus of Ota to Q-switched ruby laser treatment according to lesion colour. Br J Dermatol 2000; 142: 77-83.

21
Goldberg DJ, Stampien T. Q-switched Ruby laser treatment of congenital nevi. Arch Dermatol 1995; 131: 621-23.

22
Waldorf HA, Kauvar AN, Geronemus RG. Treatment of small and medium congenital nevi with the Q-switched ruby laser. Arch Dermatol 1996; 132(3): 301-4.

23
Grevelink JM, Van Leeuwen RL, Anderson RR, Byers HR. Clinical and histological responses of congenital melanocytic nevi after single treatment with Q-switched lasers. Arch Dermatol 1997; 133: 349-53.

24
Ara G., Anderson RR., Mandel KG, Ottesen M, Oseroff AR. Irradiation of pigmented melanoma cell with high intensity pulsed radiation generates acoustic wave and kills cells. Laser Surg Med 1990; 10: 52-9.

25
Troilius A.M. Effective treatment of traumatic tattoos with a Q-switched Nd:YAG laser. Laser Surg Med 1998; 22: 103-8.

26
Ferguson J.E., Andrew SM., Jones CJP, August PJ. The Q-switched neodynium:YAG laser and tattoo. A microscopic analysis of laser tattoo interactions. Br J Dermatol 1997; 137: 405-10.

27
Polla L, Margolis R, Dover J, Whitaker D, Murphy GF, Jacques SL, Anderson RR. Melanosomes are a primary target of Q-switched ruby laser irradiation in a guinea pig skin. J Invest Dermatol 1987; 89: 282-7.

28
Fitzpatrick R, Goldman M, Ruiz-Esparza J. Laser treatment of benign pigmented epidermal lesions using a 300nsecond pulse and 510nm wavelength. J Dermatol Surg Oncol 1993; 18: 341-7.

29
Goldman MP, Fitzpatrick RE, Satur NM, Helena I. Treatment of congenital and acquired pigmented nevi with the Q-switched alexandrite, ruby, YAG, and pigmented lesions lasers. Laser Surg Med1995; 7 (suppl.): 48.

30
Vibhagool C., Byers HR, Grevelink JM. Treatment of small nevomelanocytic nevi with a Q-switched ruby laser. J Am Acad Dermatol 1997; 36: 738-41.

31
Goldberg DJ. Congenital and acquired pigmented lesions: to treat or not to treat with lasers? Dermatol Ther 2000; 13: 60-3.

32
Stratigos AJ, Dover JS, Arndt KA. Laser treatment of pigmented lesions-2000. How far have we gone? Arch Dermatol 2000; 136: 915-21.

33
Kono T., Nozaki M., Chan HH, Sasaki K, Kwon SG. Combined use of normal mode and Q-switched ruby lasers in the treatment of congenital melanocytic naevi. Br J Plast Surg 2001; 54: 640-2.

34
Fogelman JP, Nanni CA. Treatment of hypertrichotic nevi using the 755nm long-pulsed alexandrite and 800nm diode lasers: a clinical and histologic evaluation. Interactives 24 (IC0870). 20^th World Congress of Dermatology. 1^st to 5^th July 2002. Ann Dermatol Venereol 2002; 129: 1S174.

35
Troilius A.M. Photoepilation. Courses 07 (CO1212). 20^th World Congress of Dermatology. 1^st to 5^th July 2002. Ann Dermatol Venereol 2002; 129: 1S241.

36
Menezes S., Coulomb B., Lebreton C., Dubertret L. Non-coherent near infrared protects normal human dermal fibroblast from solar ultraviolet toxicity. J Invest Dermatol 1998; 111: 629-33.

37
Maytin E. Differential effects of heat shock and UVB light upon stress protein expression in epidermal keratinocytes. J Biol Chem 1992; 267: 23189-96.

38
Barr L, Menard J. Marjolin’s ulcer. Cancer 1983; 52: 173-5.

39
Xiang L., Chan HH, Leung CK, Lai KN. The effect of sub-lethal Q-switched 755nm lasers on the expression of p16INK4A. Posters (P1251). 20^th World Congress of Dermatology. 1^st to 5^th July 2002. Ann Dermatol Venereol 2002; 129: 1S616.

40
Chan HH. Laser treatment of nevomelanocytic nevi: can results from an Asian study be applicable to the white population. Arch. Dermatol 2002; 138: 535.

41
Watanabe S, Anderson R, Brorson S, Dalickas G, Fujimoto J, Flotte T. Comparative studies of femtosecond to microsecond laser pulses on selective pigmented cell injury in skin. Photochem Photobiol 1991; 53: 757-62.

42
Van Leeuwen RL, Dekker SW, Byers HR, Vermeer BJ, Grevelink JM. Modulation of a 4b 1 and a 5b 1 integrin expression: heterogeneous effects of Q-switched ruby, Nd:YAG, and alexandrite lasers on melanoma cells in vitro. Laser Surg Med 1996; 18: 63-71.
43
Zhu WZ, Kenealy J, Burd A. Sublethal effects of exposing the human melanoma cell line Skmel-23 to 532nm laser light. Int J Cancer 1997; 72: 1104-12.

44
Soden C.E. AAD. 2000, 9-15 March San Francisco: P581.

45
Lee PK, Rosenberg CN, Tsao H, Sober AJ. Failure of Q-switched ruby laser to eradicate atypical-appearing solar lentigo: report of 2 cases. J Am Acad Dermatol 1998; 38: 314-7.