Laser Treatment of Benign Pigmented Lesions

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Laser Treatment of Benign Pigmented Lesions
May 24,2007
Noah S Scheinfeld, MD, JD, FAAD.David Goldberg, MD
eMedicine

INTRODUCTION

Schawlow and Townes were working with microwaves in 1958 when they 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. In 1960, Maiman developed stimulated emission of a red-light beam with a wavelength of 694 nm using a ruby crystal. This was the first working laser and is the prototype from which today's lasers are derived.

Since 1960, research and technical advances have adapted lasers to dermatology. In 1963, Goldman first experimented with a normal-mode (500-microsecond pulse duration), 694-nm ruby laser pulse on human skin. The darker the skin color, the more the laser was absorbed. Based on these observations, he speculated that melanin selectively absorbs laser light.

In later studies, Goldman used a Q-switched ruby laser (50-microsecond pulse duration) and found that the damage threshold of pigmented lesions was independent of skin color. This suggested a more selective effect, perhaps at the level of the melanosome. The early work with the ruby laser consisted of ablation techniques. Little bleeding was noted after nonspecific damage to the superficial dermal layers. Small areas of skin could be treated with high-intensity radiation with few complications.

Approximately 20 years later, Polla et al1 and Dover et al2, in separate studies, demonstrated that the Q-switched ruby laser targeted individual melanosomes. Electron microscopic analysis of these thermally damaged targeted melanosomes revealed membrane disruption and disorganization of the internal contents. The destruction of melanosomes is pulse-widthÒdependent; pulse durations of 40 nanoseconds and 750 nanoseconds both disrupt melanosomes, but longer pulse durations (eg, 400 microseconds) do not damage the melanosomes. This is consistent with the theory of selective photothermolysis, which states that the pulse duration of an emitted laser wavelength must be less than the thermal relaxation time of the targeted object. A typical 1-µm melanosome has a thermal relaxation time of 0.5-1 microseconds.

The cause of melanosomal destruction is unknown. Plasma formation probably does not occur. The peak powers produced with lasers used to interact with melanosomes are quite low for such an occurrence. More likely explanations are shockwave and/or cavitation damage, the photomechanical physical effects produced from thermal expansion, and/or the extreme temperature gradients created within the melanosome. Studies of acoustic waves generated by pulsed irradiation of melanosomes and pigmented cells support this possibility. Melanin absorbs and localizes the high-intensity irradiation from Q-switched lasers, thereby creating a sharp temperature gradient between the melanosome and its surrounding other structures. This gradient leads to thermal expansion and the generation and propagation of acoustic waves, which can mechanically damage the melanosome-laden cells.

Tissue repair following laser-induced melanosomal disruption demonstrates a 2-staged initial transient cutaneous depigmentation followed by subsequent repigmentation weeks later. Black guinea pig skin irradiated with 40-nanosecond Q-switched ruby pulses at a radiant exposure of 0.4 J/cm2 or greater whitens immediately, fades in 20 minutes, depigments 7-10 days later, and then repigments 4-8 weeks after treatment. The repigmented guinea pig skin displays a persistent leukotrichia, which can last up to 4 months after laser irradiation. Guinea pig skin exposed to a radiant exposure of less than that of the threshold exposure (<0.3 J/cm2) undergoes paradoxical melanogenesis. This may be due to either a sublethal change in the melanosome (interfering with the normal feedback inhibition of melanogenesis) or simply postinflammatory hyperpigmentation. Further studies are required to evaluate the therapeutic implications of this paradoxical reaction.

Laser irradiation leads to histologic melanosomal disruption and vacuolization of pigment-laden cells in the basal layer. Both keratinocytes and melanocytes exhibit pigment and nuclear material condensation at the periphery of laser-irradiated cells. This leads to a characteristic "ring-cell" appearance. Epidermal necrosis and regeneration of a pigmented epidermis follow over the next 7 days.

Observations of the effects on human skin are similar to those of guinea pig skin. The Q-switched ruby laser targets melanosomes. Subsequently, sloughing of the killed pigmented cells occurs. Transient hypopigmentation is followed by gradual repigmentation to the normal constitutive color. Other short-pulsed, high-fluence specific pigmented lesion lasers produce similar clinical and histologic findings in human skin.

Three action-spectrum studies have analyzed the ability of different-wavelength pulsed lasers to disrupt cutaneous pigment. Anderson et al evaluated the effects of a Q-switched Nd:YAG laser with a pulse duration of 10-12 nanoseconds, at 3 distinct wavelengths (355, 532, and 1064 nm), on a guinea pig's skin. The threshold exposure for immediate skin whitening, the sign of laser-induced melanosomal changes, required an energy fluence of 0.11, 0.2, and 1 J/cm2 at 355, 532, and 1064 nm, respectively.

These findings show that the threshold exposure dose is wavelength-dependent. Furthermore, longer wavelengths (which are less well-absorbed by melanin) require a higher energy fluence to induce these changes. At all evaluated wavelengths, electron microscopic examination revealed disrupted melanosomes within keratinocytes and melanocytes. Histologically, irradiated basal cells show a characteristic ring-cell appearance. This appearance is thought to be secondary to vacuolization and peripheral condensation of the cellular pigment. As expected, the transient, immediate whitening of the laser-treated area exhibits delayed epidermal depigmentation followed by repigmentation back to constitutive skin color.

Flashlamp-pulsed tunable lasers with a pulse duration of 750 nanoseconds also demonstrate the relationship between wavelength and whitening threshold. The threshold fluence was found to be 0.44, 0.62, 0.76, and 0.86 J/cm2 at 435, 488, 532, and 560 nm, respectively.

Finally, Sherwood et al performed an action-spectrum study of guinea pig skin using a flashlamp-pulsed tunable laser with a pulse duration of 300 nanoseconds at 5 different wavelengths (504, 590, 720, and 750 nm). They found the 504-nm wavelength produced the most pigment-specific injury because the longer wavelengths caused disruption of the basement membrane with pigmentary incontinence.

Today, numerous lasers can specifically target pigmented lesions, including red-light lasers (eg, 694-nm ruby, 755-nm alexandrite), green-light lasers (eg, 510-nm pulsed dye, 532-nm frequency-doubled Nd:YAG), and near-infrared lasers (eg, 1064 nm Nd:YAG). The wide range of 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 lesions, including the argon, krypton, copper, carbon dioxide, and, most recently, Er:YAG lasers.

The carbon dioxide 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 carbon dioxide laser appears to reduce the risk of scarring and has been used effectively to treat superficial epidermal pigmented lesions, such as solar lentigines. The Er:YAG laser also vaporizes water-containing cells and may more precisely ablate superficial layers of skin compared with the carbon dioxide laser. Note that wavelengths not selectively absorbed by melanin indiscriminately destroy pigmented and nonpigmented structures in the skin.

Alternatively, lasers with wavelengths that are both (1) preferentially absorbed by melanin over other cutaneous chromophores (eg, hemoglobin) and (2) penetrate to the depth of the targeted pigment can be used to more selectively target cutaneous pigment. Lasers emitting wavelengths of 630-1100 nm may provide selective melanosome absorption, good skin penetration because of these longer wavelengths, and selection of melanin over hemoglobin.

Pulsed lasers with appropriate wavelengths have a distinct theoretical advantage over continuous-wave devices in the selective destruction of cutaneous pigment. 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 hypopigmentation and potential scarring. Similar findings can ensue after use of the krypton (520-530 nm) and copper (511 nm) lasers.

Pigment-specific lasers can be divided into 3 categories: (1) green, (2) red, and (3) near-infrared. Green-light lasers are further subdivided into both pulsed and nonpulsed systems. Red-light lasers are subdivided into short-pulsed (Q-switched) and long-pulsed (normal-mode) systems. The currently available near-infrared laser is short-pulsed (Q-switched). Green-light lasers do not penetrate as deeply into the skin as the red-light and near-infrared lasers, owing to their shorter wavelengths. Therefore, green-light lasers are effective only in the treatment of epidermal pigmented lesions. See Media Files 1-6.

From 2001-2006, most investigators have studied and reported good effects with Q-switched lasers. Q-switched lasers are considered by some authorities to be the lasers of choice for pigmented melanocytic processes.

Note that laser treatments for congenital melanocytic nevi remain controversial because of the potential to induce malignancy or mask the development of malignancy. All discussions in this regard are speculative and parallel the general poor understanding of the natural history of the development of melanoma.

GREEN-LIGHT PULSED AND GREEN-LIGHT NONPULSED LASERS

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-nanosecond pulse of energy, whereas the frequency-doubled Q-switched Nd:YAG laser produces a 532-nm wavelength and a 5- to 10-nanosecond pulse of energy. Both lasers produce excellent results when used to treat epidermal pigmented lesions such as solar lentigines and ephelides. Because the green wavelength of these lasers is also well absorbed by oxyhemoglobin, purpura formation may occur following laser irradiation. The purpura resolves 1-2 weeks after treatment, with resolution or lightening of the clinical lesion 4-8 weeks after treatment. Purpura occasionally leads to postinflammatory hyperpigmentation.

Flashlamp-pumped pulsed dye laser treatment results in excellent clearing of epidermal pigmented lesions (eg, lentigines, ephelides, seborrheic keratoses, caf» au lait macules). In a study of 492 benign epidermal pigmented lesions in 65 patients, 50% of the treated lesions cleared completely after one treatment when treated at a fluence of 2-3.5 J/cm2. Another 33% of the treated lesions were lightened considerably. Ninety percent of treated epidermal pigmented lesions can be cleared after 3 treatments.

Treatment results can be affected by anatomic location. Although up to 90% of hand and facial lentigines may be cleared, less favorable results are usually seen following treatment of trunk or leg epidermal pigmented lesions. A typical treatment response includes purpura lasting 5-7 days, followed by subsequent sloughing of the treated lesion at 7-14 days. The underlying new skin is pink for 2-3 days but fades to normal skin color with rare textural changes or scarring.

In another study, 25 patients with solar lentigines showed excellent laser-induced clearing after 1-2 treatments. Fourteen patients with caf» au lait macules showed complete clearing after 3-6 treatments. Two patients with nevus spilus and 2 patients with Becker nevi showed clearing with up to 6 treatments. As a general rule, this laser produces a variable response in epidermal pigmented lesions such as caf» au lait macules, Becker nevi, and epidermal melasma. Epidermal postinflammatory hyperpigmentation also may respond. Dermal pigmented lesions predominantly show little to no response. Because some lesions show a variable clinical response, spot testing the treatment areas of the respective lesion may be prudent prior to engaging in a full treatment. Even when caf» au lait macules and Becker nevi show resolution after treatment, recurrences have been reported. Lesions may recur because of the impact of these lasers on melanosomes, with little effect on the pigment-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 with the use of this laser.

The Q-switched Nd:YAG laser is a solid-state, high-fluence, short-pulsed (10-20 nanoseconds) laser that emits at a wavelength of 1064 nm. By placing doubling crystals in the laser beam's path, the wavelength is effectively halved to 532 nm. Epidermal lesions such as lentigines and caf» au lait macules can be lightened considerably by the frequency-doubled Q-switched Nd:YAG. In one study, 84% of lentigines in 17 patients lightened by at least 50% after several treatments at 2-5 J/cm2. Postoperative purpura developed in all patients, and 25% of treated individuals showed transient hyperpigmentation. The degree of response to the laser at this wavelength is proportional to the amount of pigment chromophore present at the treatment site. When a high fluence is delivered through a small spot size, whitening of the skin is noted. This is then followed by pinpoint bleeding leading to a hemorrhagic crust, which falls off in 7-10 days.

Green-light nonpulsed (quasi-continuous wave) lasers

Nonpulsed, quasiÒcontinuous-wave green-light lasers such as the copper vapor (511 nm), krypton (520-530 nm), and variable pulse with potassium-titanyl-phosphate (532 nm) lasers share some characteristics with the aforementioned pulsed lasers. However, because the thermal relaxation time of the melanosome is exceeded using these lasers, they do not produce the same consistent clinical results. Although small epidermal pigmented lesions may be successfully cleared, more treatment sessions are usually necessary to achieve similar results to those seen with pulsed green lasers. Others have tried robotized scanning devices to allow occasional effective treatment of larger lesions such as caf» au lait macules. These lasers are not useful in the treatment of dermal pigmented lesions such as nevi of Ota. Note that the epidermal pigmented lesion response following treatment with a noncoherent flashlamp intense pulsed light source is somewhere between that of the pulsed lasers and that of nonpulsed systems.


RED-LIGHT PULSED LASERS

The 2 currently available red-light pulsed pigmented lesion lasers are the Q-switched ruby and Q-switched alexandrite lasers. The Q-switched ruby laser emits a 694-nm beam with a 20- to 50-nanosecond pulse duration. The Q-switched alexandrite laser emits a 755-nm wavelength with a pulse duration of 50-100 nanoseconds. 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.

Q-SWITCHED RUBY LASER AND Q-SWITCHED ALEXANDRITE LASER

Rapidly pulsed Q-switched lasers produce ultrashort energy bursts effective at lightening brown, blue, and black macules. The use of Q-switching laser pulses initially involved the Q-switched ruby laser. Subsequently, the Q-switched Nd:YAG laser (532 nm and 1064 nm) and the Q-switched alexandrite laser (755 nm) were used for similar purposes.3

The pulse duration of Q-switched pulses lasts nanoseconds. Their effects might involve photoacoustic causal damage of melanosomes. Melanosomes are 0.7 µm in diameter in types I and II skin and 1 µm or more in diameter in darker skin types. Melanosomes, due to their small size, have very short thermal relaxation times. Q-switched lasers, with pulses in the nanosecond range, provide the most destructive effects on melanosomes with the least damage to surrounding cellular structures.

In 2001, Suh et al4 reported 71 Korean adult patients with superficial pigmented lesions (lentigines and solar lentigines) who demonstrated a very good response rate to multiple Q-switched Nd:YAG laser treatments.

In 2003, Downs et al5 noted that the combination of the Q-switched Nd:YAG laser for caf» au lait spots, Becker nevi, speckled nevi, and congenital melanocytic nevi and the 755-nm long-pulsed alexandrite laser for hair removal effectively treated melanocytic processes in children. Congenital melanocytic nevi responded in 3 treatments; congenital hairy melanocytic nevi were treated an average of 5 times with a 50-60% lightening response in 3 of 5 cases; speckled nevus required an average of 6 treatments. Becker nevi in this study were treated as many as 8 times.

The Q-switched 1064-nm laser seems to facilitate the lowest melanin absorption and the deepest tissue penetration of the Q-switched lasers. The Q-switched Nd:YAG laser is the optimal laser for treating melanocytic processes in skin types III, IV, V, and VI, in particular for dermal processes such as the nevi of Ota or Ito. This laser can also be used to treat blue nevi. Treatment is usually performed with a 4- to 8-mm spot size at a fluence of 3-6 J/cm2.

Freckles and lentigos improve after treatment with Q-switched lasers. In 2004, Hamilton6 noted that freckles lighten with the Q-switched, 532-nm laser, usually with one treatment, but recur with solar exposure.

The Q-switched ruby laser is made with a ruby (aluminum oxide) crystal that has been grown in the presence of chromium. This combined crystal is surrounded by a helical flash lamp. The laser, in its natural state, produces a train of nonuniform pulses. In the Q-switched mode, very high peak powers (>1 X 108 W/cm2 per pulse) can be attained with each pulse. Most melanocytic processes are treated at a fluence of 4-6 J/cm2 with the Q-switched ruby laser.

Ruby laser light penetrates approximately 1 mm into the skin, is well absorbed by melanin, and is minimally absorbed by hemoglobin. Thus, this laser can be used for dermal pigmented lesions while avoiding vascular dermal structures. Epidermal pigmented lesions (eg, lentigines, ephelides) usually clear after 1-4 treatments with the Q-switched ruby laser. Taylor et al7 reported 29 lentigines that totally cleared after only one treatment. Caf» au lait macules, nevus spilus, and Becker nevi also may respond to treatment with this laser. Ashinoff et al8 treated 15 caf» au lait macules and found significant lightening after an average of 6 treatments. Frequent recurrences are the general rule after treatment of caf» au lait macules, nevus spilus, and Becker nevi.

The Q-switched ruby laser is highly effective in treating dermal pigmented lesions (eg, nevus of Ito and Ota). The long wavelength successfully targets the deep spindle cellÒshaped dermal melanocytes. Histologically, they appear to be destroyed. Geronemus9 treated 15 patients with nevus of Ota up to 7 times with the Q-switched ruby laser. Complete clearing was noted in 4 patients, with significant lightening in the others. Taylor et al10 treated 9 patients with nevus of Ota and had similar excellent results. In a large Japanese study, more than 100 individuals were treated with the Q-switched ruby laser. In this study, the degree of lightening was related to the number of treatments. Total clearing was seen in all individuals treated at least 4 times.

Lower eyelid hyperpigmentation secondary to dermal pigmentation may respond to treatment with the Q-switched ruby laser. Several treatments are usually required. Mixed epidermal and dermal lesions (eg, postinflammatory hyperpigmentation, melasma) respond better to this laser than the green pulsed lasers; however, the results remain somewhat variable.

Acquired bilateral nevi of OtaÒlike macules (Hori nevi) manifest as dermal pigmented macules. Hori nevi occur most frequently in middle-aged Asian women. In 2003, Manuskiatti et al11 reported the efficacy of Q-switched ruby laser for lightening of Hori nevi. They noted the beneficial effects of epidermal ablation using the scanned carbon dioxide laser before the Q-switched ruby laser. Approximately 15% of patients experienced hypopigmentation at 3-month follow-up, but none had hypopigmentation at 16 months.

The Q-switched ruby laser may be used in the treatment of congenital nevi. Although occasional significant clinical lightening may occur, recurrence of pigmentation is the general rule. Histologically, residual nevomelanocytes were seen in the deeper dermis. Note that some controversy remains about the long-term effect of laser treatment on the melanocytes contained within a congenital nevus. Despite this controversy, a case of Q-switched ruby laserÒinduced melanoma in a previously laser-treated congenital nevus has never been documented.

In 2003, Westerhof and Gamei12 reported that the Q-switched ruby laser demonstrated excellent effects at completely removing flat (nonpalpable) acquired junctional melanocytic nevi, but not compound nevi. Westerhof and Gamei12 noted that 1-3 treatments yielded good effects and did not result in scarring or adverse pigmentary alterations.

The Q-switched alexandrite laser is a solid-state laser, which emits light at 755 nm with a pulse duration of 50-100 nanoseconds. Fewer data have been published about this laser compared with the Q-switched ruby laser. However, because the wavelength and pulse duration are similar to those of the Q-switched ruby laser, results should be somewhat similar. A good response has been seen in the treatment of lentigines and caf» au lait macules. Dermal pigmented lesions (eg, nevi of Ota) also respond.

In one study by Rosenbach et al13, the Q-switched alexandrite laser was compared with the Q-switched Nd:YAG laser (1064 nm) for the treatment of benign melanocytic nevi in 18 patients. Both lasers produced significant improvement after 3 treatments, although the Q-switched alexandrite laser was slightly more effective. Twelve-month follow-up of 12 of the treated patients showed no evidence of recurrence or pigment darkening.

Because of its high melanin absorption, permanent hypopigmentation more commonly manifests with the Q-switched alexandrite laser than with other Q-switched lasers operating at different wavelengths.

In 2005, Kim and Kang14 reported on the treatment of congenital nevi with the Q-switched alexandrite laser in a Korean population with and without intermittent use of a carbon dioxide laser. They concluded that the Q-switched alexandrite laser worked similarly to other Q-switch mode lasers to lighten congenital melanocytic nevi but that repigmentation commonly recurred months after treatment Kim and Kang treated 37 patients with the Q-switched alexandrite laser alone and 16 patients also with carbon dioxide laser treatment between Q-switched alexandrite laser treatments. Treatment using the Q-switched alexandrite laser and carbon dioxide laser resulted in a substantially enhanced improvement score (3.06 +/- 1.18) as contrasted to persons exposed to the Q-switched alexandrite laser alone (2.43 +/- 1.07; P = .0393).

Kim and Kang14 noted adverse effects with treatment. Thirty-five nevi (67.3%) had textural changes to the skin, 2 nevi (3.8%) had depressed scar formation, 4 nevi had (7.5%) hypertrophic changes, and 12 nevi (23%) showed no changes. Forty-eight weeks after the final Q-switched alexandrite laser treatment, hypopigmentation was noted in 16 patients (30%) and hyperpigmentation was seen in 15 patients (28%). Repigmentation to a brown-to-black macule occurred in 44 (83%) of 53 patients. The mean period for this to occur was 5.45 +/- 3.93 months.

NORMAL-MODE ALEXANDRITE AND RUBY LASERS

Recently, long-pulsed ruby (300- to 3000-microsecond pulses) and alexandrite (2- to 20-microsecond pulses) lasers were shown to be effective in the treatment of Q-switched ruby laserÒresistant congenital nevi and other pigmented lesions. These lasers also may be of use in laser-assisted hair removal.

The normal-mode alexandrite laser emits light at a wavelength of 755 nm with 2- to 20-microsecond pulse durations. This laser is effective in removing pigmented hair. No data have been published on its use in pigmented lesions.

The normal-mode ruby laser is also highly effective for removing pigmented hair. The Japanese have the only published experience with the use of long-pulsed lasers for pigmented lesions. Congenital nevi treated 4 times showed significant clearing of pigmentation. Treated skin was almost indistinguishable from the normal surrounding skin.

Wang et al15 compared the Q-switched alexandrite laser to intense pulsed light in the treatment of freckles and lentigines. They found that the Q-switched alexandrite laser was superior to intense pulsed light for freckle treatment but that the intense pulsed light was preferred for lentigines in Asian persons.

Kagami et al16 found the Q-switched alexandrite laser was not a useful treatment for nevus spilus or caf» au lait spots

Geist and Phillips17 noted the development of chrysiasis after Q-switched ruby laser treatment of solar lentigines.

NEAR-INFRARED PULSED LASERS

The Q-switched Nd:YAG laser produces a 1064-nm wavelength beam with a pulse duration of 10 nanoseconds. Melanin does not absorb the 1064-nm wavelength well. Thus, the 1064-nm wavelength is not ideal for the treatment of benign pigmented lesions. Despite less absorption of this wavelength by melanin compared with the green- and red-light lasers, its advantage lies in its ability to penetrate more deeply into the skin (up to 4-6 mm). This laser may be more useful in the treatment of lesions in individuals with darker skin tones. Similar to the Q-switched ruby and alexandrite lasers, the Q-switched Nd:YAG laser is highly effective for clearing nevi of Ota. Histologically, the findings at 1064 nm are identical to those of the Q-switched ruby laser. Ring cells representing vacuolated pigmented cells with peripheral condensation of pigment are detected in the epidermal basal cell layer.

NONSELECTIVE LASER TECHNIQUES: CARBON DIOXIDE AND ERBIUM:YAG LASERS

The carbon dioxide laser (10,600 nm) and the Er:YAG laser (2940 nm) emit infrared laser energy. The Er:YAG laser produces much less thermal damage than is seen with the carbon dioxide laser. Nevertheless, even the carbon dioxide laser, when used with a low fluence, produces only limited thermal necrosis.

In a study evaluating carbon dioxide laser treatment of 146 solar lentigines, 10% cleared completely and two thirds lightened considerably. Thermal damage occurred in the basal cell layer (vacuolization and spindling of the melanocytes and keratinocytes). This damage led to epidermal necrosis 24 hours later with subsequent dermal-epidermal separation. Minimal dermal thermal damage occurred. Sloughing of the damaged epidermis was followed by subsequent reepithelialization.

CONCLUSION

Several pigment-specific lasers can effectively treat epidermal and dermal pigmented lesions. Lasers are most effective in treating epidermal and dermal pigmented lesions. Lasers are most effective in treating epidermal pigmented lesions (eg, lentigines, ephelides). Variable responses can be expected in caf» au lait macules, Becker nevi, nevus spilus, and melasma. Nevus of Ota is unique in that near-total clearance is often seen after laser treatment. New, long-pulsed, pigment-specific lasers may further enhance the clinical results obtained in resistant pigmented lesions and other conditions. Future lasers for pigmented lesion treatment may selectively target melanocytes rather than melanosomes. The controversy over laser treatment of congenital nevi will be resolved once thousands of treated lesions are monitored for several decades.