LASER TREATMENT OF PIGMENTED LESIONS

David J. Goldberg, MD

lasers that can be used to treat pigment is a result of the broad absorption spectrum of melanin. Even so, other less pigment-specific lasers have been used to treat pigmented le-sions, including the COZ and argon lasers. The COZ laser exerts its effect on tissue by simple vaporization of water-containing cells. Textural skin changes and scarring may result from this nonselective destruction. A very low wattage COZ laser appears to reduce the risk of scarring and has been used effectively to treat superficial epidermal pigmented lesions, such as solar lentigines.

The green and blue light (488 and 514 nm, respectively) of the argon laser is specifically absorbed by melanin. The problem with the system is that it functions as a continuous wave laser. Thus, although this laser selectively targets the melanin chromophore, the heat produced dissipates from the absorbing melanosomes, causing thermal damage to surrounding tissue with resultant hypopig-mentation and scarring.

Lasers that produce pulses of light shorter thanthe thermal relaxation time of melanosomes arenow used to selectively destroy targetedmelanin. The process of removing pigmentedlesions using sufficiently shorter laser pulses iscalled selective photothermolysis. The targetedmelanosome selectively absorbs the laser light andthe resultant increase in temperature inducesthermal damage of

In 1958, Schawlow and Townes, working with microwaves, first proposed a technique for the generation of monochromatic radiation by stimulated emission. They produced monochromatic radiation in the infrared optical region of the electromagnetic spectrum with an alkali vapor used as the active medium. Maiman, using a ruby crystal in 1960, developed stimulated emission of a red-light beam with a wavelength of 694 nm. This was the first working laser, and it is from this prototype that today's lasers are derived. Since 1960, research and technical advances have adapted lasers to dermatology. Leon Goldman, the father of dermatologic laser surgery, published preliminary results on the effects of a ruby laser on skin diseases. Early work with the ruby laser consisted of ablation techniques. Little bleeding was noted after nonspecific damage to the superficial dermal layers, and small areas of skin could be treated with high-intensity radiation with few sequelae.

Not surprisingly, the ruby laser was found to treat pigmented lesions well owing to its ability to target melanin. Today, there are numerous lasers that can specifically target pigmented lesions, including other red light lasers (ie, alexandrite, neodymium:yttrium-aluminum-garnet [Nd:YAGI) and green light lasers (ie, 510-nm pulsed dye, 532-nm fre-quency-doubled Nd:YAG). The wide range of

the melanosome. Because this damage occurs overa time period shorter than the melanosome'sthermal relaxation time, the absorbed energy isconfined to the targeted melanin-containingmelanosomes within melanocytes andkeratinocytes. Selective destruction ofmelanosomes results without damage tosurrounding tissue structures.

The pigmented skin of guinea pigs and humanvolunteers has been shown to respond to shortlaser pulses over a wide range of visible lightwavelengths. Lasers that target pigment includethe pulsed dye (510 nm), copper vapor (511nm), krypton (520-530 nm), frequency-doubledQ-switched Nd:YAG (532 nm), 0-switchedruby (694 nm), 0

switched alexandrite (755 nm), and QswitchedNd:YAG (1064 nm). All these wavelengths caneffectively treat pigmented lesions withoutdisrupting the normal surrounding tissue.Pigment-specific lasers can be divided into threecategories: (1) green, (2) red, and (3) near-infrared. Green light lasers are further subdividedinto both pulsed and nonpulsed systems. The redand near-infrared lasers currently available arepulsed (or Q-switched) systems. Green lightlasers do not penetrate as deeply into the skin asdo the red and near-infrared lasers owing totheir shorter wavelengths. Green light lasers aretherefore effective only in the treatment ofepidermal pigmented lesions.

Figure 1. Solar lentigines prior to (A) and after (B) one treatment session with a green light pulsed laser.

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GREEN LIGHT PULSED LASERS

These lasers produce energy with pulses shorter than the thermal relaxation time of melanosomes. Examples of these lasers are the flashlamp-pumped pulsed dye and frequency-doubled Q-switched Nd:YAG lasers. The flashlamp-pumped pulsed dye laser produces a 510-nm wavelength and 300-ns pulse of energy whereas the frequency-doubled Qswitched Nd:YAG laser produces a 532-nm wavelength and 5- to 10-ns pulse of energy. Both lasers produce excellent results when used to treat epidermal pigmented lesions such as solar lentigines and ephilides. Because the green wavelength of these lasers is also well absorbed by oxyhemoglobin, purpura formation may occur following laser irradiation. The purpura resolves in 1 to 2 weeks after treatment, with resolution or lightening of the clinical lesion in 4 to 8 weeks. Occasionally, purpura leads to postinflammatory hyperpigmentation. It should be noted that these lasers produce a variable response in epidermal pigmented lesions such as cafe-au-lait macules, Becker's nevi, and epidermal melasma. Because of the variability in clinical response, testing the treatment areas of the respective lesion may be prudent prior to engaging in a full treatment. Even when cafe-au-lait macules and Becker's nevi show resolution after treatment, recurrences have been reported. Recurrences may occur because of the impact of these lasers on melanosomes, with little effect on the pig

ment-producing melanocytes. Careful sun protection may retard, but will not prevent, recurrence. Because melasma occurs secondary to a combination of genetic, sun-induced, and hormonal factors, successful laser treatment is the exception rather than the rule in this condition. The green pulsed lasers, because of their short wavelengths, do not penetrate very deeply into the dermis and are thus ineffective for treating dermal pigmented lesions (Figs. 1 and 2).

GREEN LIGHT NONPULSED (QUASICONTINUOUS WAVE) LASERS

Nonpulsed, quasi-continuous wave green light lasers such as the copper vapor (511 nm) or krypton (520-530 nm) lasers share some characteristics with the aforementioned pulsed lasers. Because the thermal relaxation time of the melanosome is exceeded using these lasers, however, they do not produce the same consistent clinical results. Although epidermal pigmented lesions may be cleared successfully with the copper vapor and krypton lasers, more treatment sessions are usually necessary to achieve lesional clearance. There is also a theoretically higher incidence of scarring when using these systems (Fig. 3).

RED LIGHT PULSED LASERS

The two currently available red light pulsed lasers are the Q-switched ruby and Q-

Figure 2. A, Cafe-au-lait macule prior to treatment with a green light pulsed laser. B, Early recurrence of cafe-au-lait macule observed 18 months after last laser treatment.

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Figure 3. A, Solar lentigines before treatment with a green quasi-continuous wave laser. B, Partial clearing seen after two treatments.

switched alexandrite lasers. The Q-switched ruby laser emits a 694-nm beam with a 20- to 50-ns pulse duration. The Q-switched alexandrite laser emits a 755-nm wavelength with a pulse duration of 50 to 100 ns. The longer wavelengths of these lasers allow deeper penetration into the dermis. Their mechanism of action on melanin-containing melanosomes and melanocytes involves selective photothermolysis, photoacoustical mechanical disruption, and chemical alteration of the target tissue. Photoacoustic mechanical disruption is caused by rapid thermal tissue expansion, creating pressure waves that fragment pigment particles in the dermis. Within the dermis, absorption of the laser energy by melanin-rich stage III and IV melanosomes causes selective pigment destruction.

These lasers can also be used to treat epidermalpigmented lesions without purpura formationowing to the relative lack of hemoglobinabsorption at these wavelengths (Figs. 4 and 5).The major benefit of the red light systems overgreen light lasers is their efficacy in thetreatment of dermal pigmented lesions such ascongenital nevi and nevi of Ota. Although theselasers are uniformly successful in the treatment ofnevus of Ota, the response to laser treatment ofcongenital nevi is more variable. In both clinicalentities, the lasers appear to destroy some butnot all of the involved melanocytes. Darkercongenital nevi in younger patients appear toshow the best response; however, pigmentrecurrence is common. Nevi of Ota aretypically very responsive to laser treatment, withrare to no

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Figure 4. Solar lentigo prior to (A) and after (B) treatment with a red light pulsed laser.

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Figure 5. Cafe-au-lait macule on the right cheek before (A) and after (B) treatment with a red light pulsed laser. Lesion showed no evidence of recurrence 1 year after final treatment.

recurrences seen (Figs. 6 and 7). The re-sponses of dermal melasma are quite variable, with repigmentation or pigmentary worsening a common occurrence.

Recently, long-pulsed ruby lasers (300-700 µs pulses) have been shown to be effective in the treatment of Q-switched ruby laserresistant congenital nevi. These lasers may also be of use in laser-assisted hair removal (see the article by Dr. Wheeland elsewhere in this issue).

NEAR-INFRARED PULSED LASERS

The Q-switched Nd:YAG laser produces a1064-nm wavelength beam with a pulse duration of10 ns. Despite less absorption of this wavelengthby melanin compared with the green and redlight lasers, its advantage lies in its ability topenetrate more deeply in the skin. In addition,it may prove to be more useful in the treatmentof lesions in individuals with darker skin tones. Likethe Qswitched ruby and alexandrite lasers, the Q-switched Nd:YAG laser is highly effective inclearing of nevus of Ota. When used in com-bination with a carbon-containing topical sus-pension, the Nd:YAG laser may also effectivelyremove unwanted hair (Fig. 8). Because carbon-coated hair, rather than the melanin of pigmentedhairs, is the absorbing chromophore, bothpigmented and nonpigmented hairs may betreated (see the article by Wheeland).

LASER TREATMENT PROTOCOL

Green Light Lasers

Pulsed Dye (510 nm) Laser

Treatments are usually initiated at 2.0 to 3.0J/cm2 using nonoverlapping 5-mm laser spots. Animmediate ash-white tissue response shouldoccur. Repeat treatments are delivered at 6- to 8-week intervals. Solar lentigines typically requireone to two laser treatments, whereas cafe-au-laitmacules may require 2 to 12 treatment sessions.

Frequency-Doubled Nd: YAG (532 nm) Laser

Solar lentigines and cafe-au-lait macules aretypically treated at fluences of 2.0 to 2.5 J/cm2

using 1- to 3-mm spots at 10 Hz. Like the pulseddye laser, only a couple of laser sessions areneeded to treat lentigines. The response of cafe-au-lait macules is variable.

Quasi-Continuous Wave Copper Vapor (511 nm) and Krypton (520-530 nm) Lasers

The copper vapor laser is used at 0.16 to 0.25 Wusing a 150-µm spot at 0.2-second intervals. Thekrypton laser is operated at 700 mW with a 0.2-second pulse and 1-mm spot. These lasers can beused to treat solar lentigines, but their use incafe-au-lait macules has

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Figure 6. Nevus of Ota prior to (A) and after (B) treatment with a red light pulsed laser.

Figure 7. Congenital pigmented nevus prior to (A) and after (B) several treatment sessions with the Q-switched ruby laser.

Figure 8. Terminal hairs prior to (A) and 8 weeks after (B) treatment with a topical carbon-containing suspension and Q-switched Nd:YAG laser irradiation. No hair regrowth is seen.

commonly led to textural changes following treatment.

Red and Infrared Light Lasers Q-Switched Ruby Laser (694 nm)

Fluences of 5.0 to 6.0 J/cm2 are used to treat epidermal and dermal pigmented lesions. One or two treatments effectively clear lentigines whereas cafe-au-lait macules and nevi of Ota require four or more treatments at bimonthly intervals. Significant lightening of infraorbital hyperpigmentation can be achieved within two laser sessions.

Q-Switched Alexandrite Laser (755 nm)

Fluences of 6.0 to 7.0 J/cm2 are used to treat nevi of Ota, melanocytic nevi, and infraorbital

hyperpigmentation. Treatment sessions are scheduled at 6- to 8-week intervals with an average of five treatments required to effect clearance of nevus of Ota. Three treatments produce significant clearing of melanocytic nevi, whereas two sessions can significantly lighten infraorbital hyperpigmentation. Q-Switched Nd: YAG Laser (1064 nm)

Energy densities averaging 8.0 J/cm2 using a 3-mm spot size are required to treat nevus of Ota. Similar parameters are used to treat benign melanocytic nevi; however, lower fluences are used for infraorbital hyperpigmentation.

SUMMARY Several pigment-specific lasers can effectively

treat epidermal and dermal pigmented

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lesions without complications using the basicprinciples of selective photothermolysis. Althoughsuch pigmented lesions as solar lentigines andnevi of Ota are relatively easy to treat usingpigment-specific laser technology, cafe-au-laitmacules and melasma show variable responsesto treatment. New, longpulsed pigment-specificlasers may prove to further enhance the clinicalresults obtained in resistant pigmented lesionsand other conditions.

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Address reprint requests to David J. Goldberg, MD

390 Old Hook Road Westwood, NJ 07675