357
J. Photochem. Photobiol. B: Biol., 16 (1992) 357-365
Monoline argon laser (514 nm) treatment of benign pigmented lesions with long pulse lengths M. A. Trelles,
W. Verkruysse,
J. W. Pickering,
M. Vtlez,
J. Sanchez
and P. Sala
Institute Midico Wafortuny, E-43850 CambrilslTarragona (Spain)
(Received June 2, 1992; accepted June 25, 1992)
Abstract A dichroic filter was adjusted in order to make use of the green line of an argon laser for the treatment of pigmented lesions (actinic and senile lentigo, ephelis, cafe-au-lait marks and spilus nevus). Using a power of 1.5 W, a spot size of 0.5 mm and pulse lengths of 200 or 300 ms, satisfactory elimination of 620 pigmented cutaneous lesions was achieved. Although the pulse lengths used were much longer than the thermal relaxation time of the melanosomes, the histology after treatment showed little damage of adjacent structures. Good restoration of the epidermis and a return of normal pigmentation led to excellent cosmetic results, with few complications.
Keywords: Argon laser, pigmented
lesions, melanosomes.
1. Introduction
Cutaneous alterations due to large concentrations of melanin are mainly a result of excessive exposure to UV light, genetic influence and congenital factors. Normally, pigment-producing cells are positioned at the basal layer of the epidermis. The main functions of the epidermis are to protect the body against infections, dehydration and excessive irradiation by UV light (wavelengths shorter than 400 nm). Melanin is stored in small (approximately 0.5 pm) sacs, called melanosomes. Benign pigmented lesions appear dark because of an increased amount of melanocytes, an overproduction of melanosomes or a combination of these. For example, ephelis, spilus nevus and cafe-au-lait marks are characterized by localized areas of overactive melanocytes which are present in an approximately normal number in the basal layer of the epidermis. Lentigos, however, usually show not only an increased number of melanocytes in the basal layer but also a proliferation into other epidermal layers. Other histological characteristics of lentigo are accentuated ridges of the epiderm (lentigo simplex) or irregular, club-shaped epidermal ridges (senile lentigo). In intradermal pigmented lesions the amount of melanosomes is not only increased in the epidermis but also in the dermis to depths up to several hundreds of micrometres. Selective photothermolysis to treat these lesions was first proposed by Anderson and Parrish [l]. The main targets for photocoagulation in the laser treatment of pigmented lesions are the melanosomes and melanocytes. Due to their role in protecting the organism against UV light, the absorption of light by melanin is very high in this wavelength region. The absorption of visible light (longer wavelengths) by melanin is
loll-1344/92/$5.00
0 1992 - Elsevier Sequoia. All rights reserved
358
lower but still much higher than that of adjacent tissue. Therefore this light can also be used to damage selectively the melanosomes. Although a large variability in values has been reported [2], the absorption coefficient of melanosomes for blue and green light may be estimated to be several hundreds of reciprocal centimetres. The results presented in this report show a high absorbance of green light by melanin. To photothermolyse selectively the melanosomes, two main conditions are required: selective light absorption by the target and a pulse length shorter than the thermal relaxation time of the target [l]. Long illumination times lead to the conduction of a considerable part of the heat to adjacent structures which significantly decreases the selectivity of the photothermolysis. When the pulse length is longer than the thermal relaxation time of the target, a considerable amount of heat will be conducted to surrounding tissue possibly leading to damage of these tissues. Research into selective photothermolysis and treatment of pigmented lesions has been performed using various short-pulse lasers, such as COZ (10 600 nm) [3], Nd:YAG (1060, 532 and 355 nm) [4-6], excimer (351 nm) [7], Q-switched ruby (694 nm) [8, 91 and argon (488, 514 nm) lasers [9]. At the Instituto Medico Vilafortuny we have considerable experience in the elimination of various pigmented lesions by mechanisms other than selective photothermolysis. Despite experiments and theoretical modelling which indicate that short pulse lengths (around 1 ps) are optimal to target selectively the melanosomes, we present satisfactory results achieved with a continuous wave argon laser (514 nm) with a spot size of 0.5 mm and pulses of 200-300 ms.
2. Materials
and methods
186 patients presented 620 pigmented lesions which were treated between December 1987 and January 1990. The different types of pigmented lesions are given in Table 1. The number of pigmented lesions per patient varied between 2 and 6. An argon ion laser was used (Supergraphite CR-B, Coherent Ltd., USA) with a maximum power of 27 W. The green line (514 nm) was selected from the multiline beam, using a dichroic filter. Although green light is only slightly better absorbed than TABLE 1 Different types of pigmented lesion treated between December 1987 and January 1990 and the number of patients presenting them. In total, 620 pigmented lesions were treated in this period (180 patients) Lesion
Number
Actinic lentigo Senile lentigo Lentigines Ephelis Caf&au-lait marks Naevus of Becker Spilus nevus Basal melanosis (epiderm) Residual melanosis (post-treatment)
42 59 5 7 34 4 14 6 15
of patients
359
blue light (488 nm), we observed a larger degree of carbonization at the lesion surface when green light (514 nm) is used. An optical shutter was used to obtain light pulses of 200 or 300 ms with 300 ms intervals. The light beam was passed through a fibre and was focused to a spot size of 0.5 mm. The power output was measured with a power meter (Labmaster-E, Coherent, USA) and the input power was adjusted until the power at the fibre tip was measured to be 1.5 W. In most patients (78%; 140 patients), anaesthesia was not necessary. When needed, the local anaesthetic applied was Mepivancaina 2%, without vasoconstrictor, in quantities varying between 1 and 4 ml. Approximately 3 min after injection of the anaesthetic the treatment was started. To decide between a pulse length of 200 ms or 300 ms we estimated the depth of the pigment by looking at the colour and characteristics of the lesion surface. If the colour was pale and the lesion was flat we interpreted it to be relatively superficial and the shorter pulse length of 200 ms was chosen to limit the depth at which damage was caused. After having irradiated the whole area, it is possible to remove the necrotized epidermis with a wet gauze. If necessary, in elevated lesions, a second layer can be irradiated and removed in the same way. After the wound has been cleaned this procedure may be repeated until the level of the surrounding tissue is equalized. Immediately after treatment the skin was cooled quasi-continuously with Chloroethylene Chemirosa (Laboratorios ERN s.a., Barcelona) to prevent blistering. If the patient reported discomfort, the cooling was immediately stopped. Up to 1 week after treatment a cream composed of Flupamesona with Gentamicin and sterilized Vaseline was used on the treated areas as an anti-inflammatory and rehydration aid.
3. Results 3.1. Clinical During irradiation the temperature in the tissue quickly reaches high values. If the temperature exceeds 100 “C the pathological effects in the tissue are dominated by its water content (around 75%). At 100 “C the water is vaporized and forms small vacuoles in which high pressures of gas are established. In spite of the beam being focused to a spot size of only 0.5 mm in diameter, the heat effect exceeded this diameter. Irradiation of spots separated by approximately 1 mm appeared to affect the intermediate tissue. A thin layer of carbonized material appeared at the irradiated spot. One or two treatments were required to blanch the pigmented lesions satisfactorily. Normally several months separated two treatments. Of 186 patients only one required four treatments. 3.2. Follow up The results were subjectively assessed, in cooperation with the patient, and registered on a scale giving four values of success: very good, good, fair and bad (Fig. 1). In most patients, the hair follicles were not irreversibly damaged as, a few weeks after treatment, normal hair appeared on the treated spot. Only in a few patients were cicatricial complications, erythrocis or hypopigmentation observed during the recovery of the epidermis, and up to 2 years after treatment (Table 2), and practically all patients (98%) recovered very satisfactorily. In 8% of
360
MONOLINE 514 Ar+ Pigmented Lesion / RESULTS 160 patients / 620 lesions --
-Very
Qood/Muy
bien
Gaod/Bien
a Hypertrophic
Fslr/Regular
scar in an actinic
Bad/Ma1
naevi
Fig. 1. Subjective results, assessed in cooperation with the patients, 1 year after treatment. Fair or bad results do not necessarily refer to all the lesions eliminated in a patient but, in general, to one or two of the average of 4-6 lesions present.
TABLE 2 Cicatricial complications. The complications were observed during the treatment of some but not all lesions on each patient, nor necessarily over the whole lesion surface. The number of lesions per patient varied between 2 and 6 Lesion
Complications
Actinic lentigo Senile lentigo Lentigines Ephelis Cafe-au-lait marks Naevus’ of Becker Spilus nevus Basal melanosis (epiderm) Residual melanosis (post-treatment)
9 6 3 1 11 0 0 1 2
Most frequent complications: hypopigrnentation (4); hypertrophic scar (1); hypotrophic scar (1); erythrocis (cuperosis) (14); residual pigmentation (6); total recurrence (3); partial recurrence (8).
361
the lesions, remaining pigment was seen after the first treatment, which was elimil nated in consecutive treatments. During the follow up of 2 years, in most patients, a good skin texture was mainti ained without recurrence of the pigmented lesion (Figs. 2-5).
4. Discussion In general, in the medical literature, practically all the reported t reatments have been performed using very small pulse lengths [4-91 (several tenths tof nanosec :onds to microseconds) from pulsed (dye) lasers. The corresponding energy densities were
Fig. 2.
Senile lentigo on the hand. Before treatment.
Fig. 3. Senile
lentigo
as shown
in Fig. 2, 8 weeks
after treatment.
362
Fig. 4. Pigmented
cellular naevi on the left cheek and upper lip. Before treatment.
Fig. 5. The lesions shown in Fig. 4, 4 years after treatment. typically around 1 J cm-‘. Several studies have shown melanosomes to be suitable targets for selective photothermolysis at various wavelengths when irradiated using submicrosecond pulses [2, 10-121. The important difference between the parameters used in this study and those used in most of the literature on pigmented lesions is the pulse length. Although the pulse lengths of 200 and 300 ms are more than a factor of 200 000 longer than the estimated relaxation time for melanosomes, we achieved excellent results in treating different types of pigmented lesion. It is obvious that a damage
363
mechanism different from selective photothermolysis plays a role in the elimination of pigmented lesions using these parameters. During these relatively long pulses, a considerable part of the heat is conducted away from the target to surrounding structures and general heating results. Although a relatively low power is used (1.5 W), the combination of a spot size of 0.5 mm and a pulse length of 200 or 300 ms leads to very high energy densities. Two main effects result from irradiation using these parameters: (1) a coagulated and necrotized layer, and (2) an underlying area which is only partially coagulated, The superficial layer is removed with a gauze. A number of melanosomes and melanocytes are removed together with this necrotized layer and, in the underlying area, more melanosomes and melanocytes are destroyed by coagulation. However, not all melanocytes are destroyed (Figs. 6 and 7). In the weeks following treatment, the wound heals by restoration of the dermis and formation of a new epidermal layer and, ideally, the new epidermis is normally pigmented. Hyperpigmentation, which characterized the pigmented lesion before treatment, was successfully eliminated by our treatment and hypopigmentation was seen in only four lesions (1%). The healing of the lesion with good pigmentation may be due to the incomplete elimination of melanocytes. Hypopigmentation is often seen when a COz laser is used for the treatment of macular pigmented lesions, because the vaporization of the tissue includes all layers at which melanocytes are located. Although a considerable amount of tissue is vaporized during equalization of the area of the lesion to the surrounding tissue in our method, the relatively deeply situated nests of pigmented cells in the dermis are not damaged. Therefore the green light of the argon ion laser avoids both hypopigmentation and recurrence. The green light of the argon ion laser penetrates more deeply into the tissue than the IR light produced by CO1 lasers, which is absorbed by water in the superficial tissue layers. Consequently, these layers are vaporized in contrast with structures
Fig. 6. Pigmented intradermal lesion (haematoxylin-eosin) large amounts at both the basal layer of the epidermis accentuated rete ridges of the epidermis.
(X 100). Melanocytes are present in and in the dermis. Note the large,
Fig. 7. The same pigmented lesion as shown in Fig. 6, 2 weeks after laser treatment (haematoxylin-eosin) (X 400). The number of melanocytes has decreased both in the basal layer and the dermis.
364
situated more deeply in the skin layers. As the argon laser light is hardly absorbed by normal dermal tissue, it is mainly absorbed by melanosomes and melanocytes and is more selective than the CO2 laser. During the relatively long pulses, some of the heat produced diffuses away to the surrounding tissues. As a result of both the heat diffusion and light diffusion through scattering, the amount of irreversibly damaged melanocytes gradually decreases with depth. The partial elimination of melanocytes seems to be a crucial factor in this mode of treatment. The remaining melanocytes, although they may be lower in number than normal, produce enough melanin to repigment the newly formed epidermis, during and after the healing period, resulting in equal pigmentation with the surrounding tissue. In fact, from histology, it is known that the remaining melanocytes increase their melanin production in a type of compensatory mechanism. Other mechanisms of repigmentation may be involved in those areas in which melanocytes have been removed or destroyed [13]. Treatments with short-pulse lasers may be theoretically safer, but these lasers are not commonly available in hospitals or clinics. In contrast, the argon laser is a common tool in dermatology. Furthermore, by using the described method, excellent results can be achieved in one or two treatments; this is clearly advantageous to dye laser treatment using short pulses, as usually three to four treatments are required before satisfactory results are achieved [14]. References 1 R. R. Anderson and J. A. Parrish, Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation, Science, 220 (1983) 524-527. 2 S. L. Jacques and D. J. McAuliffe, The melanosome: threshold temperature for explosive vaporisation and internal absorption coefficient during pulsed laser irradiation, Photochem Photobiol., 6 (1991) 769-775. 3 S. Watanabe, R. R. Anderson, S. Brorson, G. Dalickas, J. G. Fujimoto and T. J. Flotte, Comparative studies of femtosecond to microsecond laser pulses on selective pigmented cell injury in skin, Photochem. Photobiol., 53 (1991) 757-762. 4 R. Bilik, S. Kahanovich, M. Ruboin, A. Rothem, I. Geiemter and I. Kaplan, Morbidity and recurrence rates after surgical treatment of malignant melanoma by scalpel versus CO2 laser beam, Surg. Gynecol. Obstet., 165 (1987) 333-338. 5 L. Goldman, G. Nath, G. Schindler, J. Fidler and R. J. Rockwell, ‘High-power NeodymiumYAG laser surgery’ Acru Dem.-Venereol., 53 (1973) 4549. 6 R. R. Anderson, R. J. Margolis, S. Watanabe, T. Flotte, G. J. Hruza and J. S. Dover, Selective photothermolysis of cutaneous pigmentation by Q-switched Nd:YAG laser pulses at 1064, 532 and 355 nm, J. Invest. Dennatol., 93 (1989) 28-32. 7 R. J. Lane, R. Linsker, J. J. Wynne, A. Torres and R. G. Geronemous, Ultrtraviolet laser ablation of skin, Arch. Dematol., 121 (1985) 609417. 8 J. S. Dover, R. J. Margolis, L. L. Polla, S. Watanabe, G. J. Hruza, J. A. Parrish and R. R. Anderson, Pigmented guinea pig skin irradiated with Q-switched ruby laser pulses, Arch. Dermatol., 125 (1989) 4349. 9 T. Ohshiro and Y. Maruyama, The ruby and argon lasers in the treatment of naevi, Ann. Acad. Med. Singapore, I2 (1983) 388-395. 10 L. L. Polla, R. J. Margolis, J. S. Dover, D. W. Whitaker, G. F. Murphy, S. L. Jacques and R. R. Andersson, Melanosomes are a primary target of Q-switched ruby laser irradiation in guinea pig skin, J. Invest. Dermatol., 89 (1987) 281-286. 11 J. A. Parrish, R. R. Anderson, T. Harris& B. S. Paul and G. F. Murphy, Selective thermal effects with pulsed irradiation from lasers: from organ to organelle, J. Invest. Dermatol., 81 (1983) 333-336.
365 12 G. Ara, R. R. Anderson, K. G. Mandel, M. Ottesen and A. R. Oseroff, Irradiation of pigmented melanosome cells with high intensity pulsed radiation generates acoustic waves and ‘kills cells, Lasers Surg. Med., IO (1990) 52-59. 13 A. H. Mehregen, Pinkus Guide to Dermatohistopathology, Appleton-Century-Crofts, Norwack, CT, 4th edn., 1986, p. 368. 14 Candela Corporation, Commercial Brochure for the 510 nm t?tlsed Dye Laser with Nanosecond Pulses. 1991.
J. Photochem. Photobiol. B: Biol., 16 (1992) 357-365
Monoline argon laser (514 nm) treatment of benign pigmented lesions with long pulse lengths M. A. Trelles,
W. Verkruysse,
J. W. Pickering,
M. Vtlez,
J. Sanchez
and P. Sala
Institute Midico Wafortuny, E-43850 CambrilslTarragona (Spain)
(Received June 2, 1992; accepted June 25, 1992)
Abstract A dichroic filter was adjusted in order to make use of the green line of an argon laser for the treatment of pigmented lesions (actinic and senile lentigo, ephelis, cafe-au-lait marks and spilus nevus). Using a power of 1.5 W, a spot size of 0.5 mm and pulse lengths of 200 or 300 ms, satisfactory elimination of 620 pigmented cutaneous lesions was achieved. Although the pulse lengths used were much longer than the thermal relaxation time of the melanosomes, the histology after treatment showed little damage of adjacent structures. Good restoration of the epidermis and a return of normal pigmentation led to excellent cosmetic results, with few complications.
Keywords: Argon laser, pigmented
lesions, melanosomes.
1. Introduction
Cutaneous alterations due to large concentrations of melanin are mainly a result of excessive exposure to UV light, genetic influence and congenital factors. Normally, pigment-producing cells are positioned at the basal layer of the epidermis. The main functions of the epidermis are to protect the body against infections, dehydration and excessive irradiation by UV light (wavelengths shorter than 400 nm). Melanin is stored in small (approximately 0.5 pm) sacs, called melanosomes. Benign pigmented lesions appear dark because of an increased amount of melanocytes, an overproduction of melanosomes or a combination of these. For example, ephelis, spilus nevus and cafe-au-lait marks are characterized by localized areas of overactive melanocytes which are present in an approximately normal number in the basal layer of the epidermis. Lentigos, however, usually show not only an increased number of melanocytes in the basal layer but also a proliferation into other epidermal layers. Other histological characteristics of lentigo are accentuated ridges of the epiderm (lentigo simplex) or irregular, club-shaped epidermal ridges (senile lentigo). In intradermal pigmented lesions the amount of melanosomes is not only increased in the epidermis but also in the dermis to depths up to several hundreds of micrometres. Selective photothermolysis to treat these lesions was first proposed by Anderson and Parrish [l]. The main targets for photocoagulation in the laser treatment of pigmented lesions are the melanosomes and melanocytes. Due to their role in protecting the organism against UV light, the absorption of light by melanin is very high in this wavelength region. The absorption of visible light (longer wavelengths) by melanin is
loll-1344/92/$5.00
0 1992 - Elsevier Sequoia. All rights reserved
358
lower but still much higher than that of adjacent tissue. Therefore this light can also be used to damage selectively the melanosomes. Although a large variability in values has been reported [2], the absorption coefficient of melanosomes for blue and green light may be estimated to be several hundreds of reciprocal centimetres. The results presented in this report show a high absorbance of green light by melanin. To photothermolyse selectively the melanosomes, two main conditions are required: selective light absorption by the target and a pulse length shorter than the thermal relaxation time of the target [l]. Long illumination times lead to the conduction of a considerable part of the heat to adjacent structures which significantly decreases the selectivity of the photothermolysis. When the pulse length is longer than the thermal relaxation time of the target, a considerable amount of heat will be conducted to surrounding tissue possibly leading to damage of these tissues. Research into selective photothermolysis and treatment of pigmented lesions has been performed using various short-pulse lasers, such as COZ (10 600 nm) [3], Nd:YAG (1060, 532 and 355 nm) [4-6], excimer (351 nm) [7], Q-switched ruby (694 nm) [8, 91 and argon (488, 514 nm) lasers [9]. At the Instituto Medico Vilafortuny we have considerable experience in the elimination of various pigmented lesions by mechanisms other than selective photothermolysis. Despite experiments and theoretical modelling which indicate that short pulse lengths (around 1 ps) are optimal to target selectively the melanosomes, we present satisfactory results achieved with a continuous wave argon laser (514 nm) with a spot size of 0.5 mm and pulses of 200-300 ms.
2. Materials
and methods
186 patients presented 620 pigmented lesions which were treated between December 1987 and January 1990. The different types of pigmented lesions are given in Table 1. The number of pigmented lesions per patient varied between 2 and 6. An argon ion laser was used (Supergraphite CR-B, Coherent Ltd., USA) with a maximum power of 27 W. The green line (514 nm) was selected from the multiline beam, using a dichroic filter. Although green light is only slightly better absorbed than TABLE 1 Different types of pigmented lesion treated between December 1987 and January 1990 and the number of patients presenting them. In total, 620 pigmented lesions were treated in this period (180 patients) Lesion
Number
Actinic lentigo Senile lentigo Lentigines Ephelis Caf&au-lait marks Naevus of Becker Spilus nevus Basal melanosis (epiderm) Residual melanosis (post-treatment)
42 59 5 7 34 4 14 6 15
of patients
359
blue light (488 nm), we observed a larger degree of carbonization at the lesion surface when green light (514 nm) is used. An optical shutter was used to obtain light pulses of 200 or 300 ms with 300 ms intervals. The light beam was passed through a fibre and was focused to a spot size of 0.5 mm. The power output was measured with a power meter (Labmaster-E, Coherent, USA) and the input power was adjusted until the power at the fibre tip was measured to be 1.5 W. In most patients (78%; 140 patients), anaesthesia was not necessary. When needed, the local anaesthetic applied was Mepivancaina 2%, without vasoconstrictor, in quantities varying between 1 and 4 ml. Approximately 3 min after injection of the anaesthetic the treatment was started. To decide between a pulse length of 200 ms or 300 ms we estimated the depth of the pigment by looking at the colour and characteristics of the lesion surface. If the colour was pale and the lesion was flat we interpreted it to be relatively superficial and the shorter pulse length of 200 ms was chosen to limit the depth at which damage was caused. After having irradiated the whole area, it is possible to remove the necrotized epidermis with a wet gauze. If necessary, in elevated lesions, a second layer can be irradiated and removed in the same way. After the wound has been cleaned this procedure may be repeated until the level of the surrounding tissue is equalized. Immediately after treatment the skin was cooled quasi-continuously with Chloroethylene Chemirosa (Laboratorios ERN s.a., Barcelona) to prevent blistering. If the patient reported discomfort, the cooling was immediately stopped. Up to 1 week after treatment a cream composed of Flupamesona with Gentamicin and sterilized Vaseline was used on the treated areas as an anti-inflammatory and rehydration aid.
3. Results 3.1. Clinical During irradiation the temperature in the tissue quickly reaches high values. If the temperature exceeds 100 “C the pathological effects in the tissue are dominated by its water content (around 75%). At 100 “C the water is vaporized and forms small vacuoles in which high pressures of gas are established. In spite of the beam being focused to a spot size of only 0.5 mm in diameter, the heat effect exceeded this diameter. Irradiation of spots separated by approximately 1 mm appeared to affect the intermediate tissue. A thin layer of carbonized material appeared at the irradiated spot. One or two treatments were required to blanch the pigmented lesions satisfactorily. Normally several months separated two treatments. Of 186 patients only one required four treatments. 3.2. Follow up The results were subjectively assessed, in cooperation with the patient, and registered on a scale giving four values of success: very good, good, fair and bad (Fig. 1). In most patients, the hair follicles were not irreversibly damaged as, a few weeks after treatment, normal hair appeared on the treated spot. Only in a few patients were cicatricial complications, erythrocis or hypopigmentation observed during the recovery of the epidermis, and up to 2 years after treatment (Table 2), and practically all patients (98%) recovered very satisfactorily. In 8% of
360
MONOLINE 514 Ar+ Pigmented Lesion / RESULTS 160 patients / 620 lesions --
-Very
Qood/Muy
bien
Gaod/Bien
a Hypertrophic
Fslr/Regular
scar in an actinic
Bad/Ma1
naevi
Fig. 1. Subjective results, assessed in cooperation with the patients, 1 year after treatment. Fair or bad results do not necessarily refer to all the lesions eliminated in a patient but, in general, to one or two of the average of 4-6 lesions present.
TABLE 2 Cicatricial complications. The complications were observed during the treatment of some but not all lesions on each patient, nor necessarily over the whole lesion surface. The number of lesions per patient varied between 2 and 6 Lesion
Complications
Actinic lentigo Senile lentigo Lentigines Ephelis Cafe-au-lait marks Naevus’ of Becker Spilus nevus Basal melanosis (epiderm) Residual melanosis (post-treatment)
9 6 3 1 11 0 0 1 2
Most frequent complications: hypopigrnentation (4); hypertrophic scar (1); hypotrophic scar (1); erythrocis (cuperosis) (14); residual pigmentation (6); total recurrence (3); partial recurrence (8).
361
the lesions, remaining pigment was seen after the first treatment, which was elimil nated in consecutive treatments. During the follow up of 2 years, in most patients, a good skin texture was mainti ained without recurrence of the pigmented lesion (Figs. 2-5).
4. Discussion In general, in the medical literature, practically all the reported t reatments have been performed using very small pulse lengths [4-91 (several tenths tof nanosec :onds to microseconds) from pulsed (dye) lasers. The corresponding energy densities were
Fig. 2.
Senile lentigo on the hand. Before treatment.
Fig. 3. Senile
lentigo
as shown
in Fig. 2, 8 weeks
after treatment.
362
Fig. 4. Pigmented
cellular naevi on the left cheek and upper lip. Before treatment.
Fig. 5. The lesions shown in Fig. 4, 4 years after treatment. typically around 1 J cm-‘. Several studies have shown melanosomes to be suitable targets for selective photothermolysis at various wavelengths when irradiated using submicrosecond pulses [2, 10-121. The important difference between the parameters used in this study and those used in most of the literature on pigmented lesions is the pulse length. Although the pulse lengths of 200 and 300 ms are more than a factor of 200 000 longer than the estimated relaxation time for melanosomes, we achieved excellent results in treating different types of pigmented lesion. It is obvious that a damage
363
mechanism different from selective photothermolysis plays a role in the elimination of pigmented lesions using these parameters. During these relatively long pulses, a considerable part of the heat is conducted away from the target to surrounding structures and general heating results. Although a relatively low power is used (1.5 W), the combination of a spot size of 0.5 mm and a pulse length of 200 or 300 ms leads to very high energy densities. Two main effects result from irradiation using these parameters: (1) a coagulated and necrotized layer, and (2) an underlying area which is only partially coagulated, The superficial layer is removed with a gauze. A number of melanosomes and melanocytes are removed together with this necrotized layer and, in the underlying area, more melanosomes and melanocytes are destroyed by coagulation. However, not all melanocytes are destroyed (Figs. 6 and 7). In the weeks following treatment, the wound heals by restoration of the dermis and formation of a new epidermal layer and, ideally, the new epidermis is normally pigmented. Hyperpigmentation, which characterized the pigmented lesion before treatment, was successfully eliminated by our treatment and hypopigmentation was seen in only four lesions (1%). The healing of the lesion with good pigmentation may be due to the incomplete elimination of melanocytes. Hypopigmentation is often seen when a COz laser is used for the treatment of macular pigmented lesions, because the vaporization of the tissue includes all layers at which melanocytes are located. Although a considerable amount of tissue is vaporized during equalization of the area of the lesion to the surrounding tissue in our method, the relatively deeply situated nests of pigmented cells in the dermis are not damaged. Therefore the green light of the argon ion laser avoids both hypopigmentation and recurrence. The green light of the argon ion laser penetrates more deeply into the tissue than the IR light produced by CO1 lasers, which is absorbed by water in the superficial tissue layers. Consequently, these layers are vaporized in contrast with structures
Fig. 6. Pigmented intradermal lesion (haematoxylin-eosin) large amounts at both the basal layer of the epidermis accentuated rete ridges of the epidermis.
(X 100). Melanocytes are present in and in the dermis. Note the large,
Fig. 7. The same pigmented lesion as shown in Fig. 6, 2 weeks after laser treatment (haematoxylin-eosin) (X 400). The number of melanocytes has decreased both in the basal layer and the dermis.
364
situated more deeply in the skin layers. As the argon laser light is hardly absorbed by normal dermal tissue, it is mainly absorbed by melanosomes and melanocytes and is more selective than the CO2 laser. During the relatively long pulses, some of the heat produced diffuses away to the surrounding tissues. As a result of both the heat diffusion and light diffusion through scattering, the amount of irreversibly damaged melanocytes gradually decreases with depth. The partial elimination of melanocytes seems to be a crucial factor in this mode of treatment. The remaining melanocytes, although they may be lower in number than normal, produce enough melanin to repigment the newly formed epidermis, during and after the healing period, resulting in equal pigmentation with the surrounding tissue. In fact, from histology, it is known that the remaining melanocytes increase their melanin production in a type of compensatory mechanism. Other mechanisms of repigmentation may be involved in those areas in which melanocytes have been removed or destroyed [13]. Treatments with short-pulse lasers may be theoretically safer, but these lasers are not commonly available in hospitals or clinics. In contrast, the argon laser is a common tool in dermatology. Furthermore, by using the described method, excellent results can be achieved in one or two treatments; this is clearly advantageous to dye laser treatment using short pulses, as usually three to four treatments are required before satisfactory results are achieved [14]. References 1 R. R. Anderson and J. A. Parrish, Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation, Science, 220 (1983) 524-527. 2 S. L. Jacques and D. J. McAuliffe, The melanosome: threshold temperature for explosive vaporisation and internal absorption coefficient during pulsed laser irradiation, Photochem Photobiol., 6 (1991) 769-775. 3 S. Watanabe, R. R. Anderson, S. Brorson, G. Dalickas, J. G. Fujimoto and T. J. Flotte, Comparative studies of femtosecond to microsecond laser pulses on selective pigmented cell injury in skin, Photochem. Photobiol., 53 (1991) 757-762. 4 R. Bilik, S. Kahanovich, M. Ruboin, A. Rothem, I. Geiemter and I. Kaplan, Morbidity and recurrence rates after surgical treatment of malignant melanoma by scalpel versus CO2 laser beam, Surg. Gynecol. Obstet., 165 (1987) 333-338. 5 L. Goldman, G. Nath, G. Schindler, J. Fidler and R. J. Rockwell, ‘High-power NeodymiumYAG laser surgery’ Acru Dem.-Venereol., 53 (1973) 4549. 6 R. R. Anderson, R. J. Margolis, S. Watanabe, T. Flotte, G. J. Hruza and J. S. Dover, Selective photothermolysis of cutaneous pigmentation by Q-switched Nd:YAG laser pulses at 1064, 532 and 355 nm, J. Invest. Dennatol., 93 (1989) 28-32. 7 R. J. Lane, R. Linsker, J. J. Wynne, A. Torres and R. G. Geronemous, Ultrtraviolet laser ablation of skin, Arch. Dematol., 121 (1985) 609417. 8 J. S. Dover, R. J. Margolis, L. L. Polla, S. Watanabe, G. J. Hruza, J. A. Parrish and R. R. Anderson, Pigmented guinea pig skin irradiated with Q-switched ruby laser pulses, Arch. Dermatol., 125 (1989) 4349. 9 T. Ohshiro and Y. Maruyama, The ruby and argon lasers in the treatment of naevi, Ann. Acad. Med. Singapore, I2 (1983) 388-395. 10 L. L. Polla, R. J. Margolis, J. S. Dover, D. W. Whitaker, G. F. Murphy, S. L. Jacques and R. R. Andersson, Melanosomes are a primary target of Q-switched ruby laser irradiation in guinea pig skin, J. Invest. Dermatol., 89 (1987) 281-286. 11 J. A. Parrish, R. R. Anderson, T. Harris& B. S. Paul and G. F. Murphy, Selective thermal effects with pulsed irradiation from lasers: from organ to organelle, J. Invest. Dermatol., 81 (1983) 333-336.
365 12 G. Ara, R. R. Anderson, K. G. Mandel, M. Ottesen and A. R. Oseroff, Irradiation of pigmented melanosome cells with high intensity pulsed radiation generates acoustic waves and ‘kills cells, Lasers Surg. Med., IO (1990) 52-59. 13 A. H. Mehregen, Pinkus Guide to Dermatohistopathology, Appleton-Century-Crofts, Norwack, CT, 4th edn., 1986, p. 368. 14 Candela Corporation, Commercial Brochure for the 510 nm t?tlsed Dye Laser with Nanosecond Pulses. 1991.
