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Eighty per cent of the total emissions occur at 488 and 514 nm. These two wavelengths of light are absorbed by two chromophores in the skin: oxyhemoglobin and melanin (Fig. 2.1).

Although the argon laser wavelengths do not coincide with the absorption maxima of oxyhemoglobin, there is sufficient absorption to produce thermal damage to red blood cells in cutaneous blood vessels situated superficially within the first millimeter of the skin. Because the argon laser light is delivered in pulses lasting many tens of milliseconds (ms) there is nonspecific thermal damage to perivascular connective tissue and beyond. The unfortunate clinical consequence has been textural alteration, scarring, and pigmentary changes (Fig. 2.2)

The continuous wave argon laser beam can be mechanically shuttered to pulses of 50-

HbO,

300 400 500 600 700 Wavelength (nm)

Fig. 2.1. Schematic absorption spectrum of oxyhemoglobin (Hbo2) and melanin

300 400 500 600 700 Wavelength (nm)

Fig. 2.1. Schematic absorption spectrum of oxyhemoglobin (Hbo2) and melanin

Fig. 2.2. Adverse effects of argon laser treatment [from S.W. Lanigan (2000) Lasers in Dermatology, Springer Verlag, London]
Fig. 2.3. Immediate blanching with argon laser [from S.W. Lanigan (2000) Lasers in Dermatology, Springer Verlag, London]

100 ms or longer. Alternatively, the operator moves the beam continuously across the surface of the skin to reduce the exposure time at each unit area. The clinical end point is minimal blanching. This is a just visible grayish white discoloration of the skin (Fig. 2.3). The operator gradually increases the power until this change is observed. The visible change of minimal blanching inevitably involves nonselective thermal damage, as it is a sign of thermal coagulation of tissue protein. Treatment is far more painful than with current lasers, and generally localized areas within a PWS are treated after infiltrational anesthesia. After treatment the skin invariably weeps and crusts with some superficial blistering. The blanched appearance reverts to a reddish purple color after a few days. Gradually after a period of 4-8 weeks the treated area visibly lightens towards normal skin color. This lightening progresses for more than 6 months after treatment. Because of the high instance of adverse reactions with the argon laser, it is essential to initially perform a small test treatment. The presence of scarring in the test site would normally indicate cessation of treatment or a change to a different laser.

Results of treating PWS with the argon laser are generally better in adults with purple PWS. Seventy per cent of adult patients will obtain good to excellent results. Hypertrophic scarring after argon laser treatment of PWS ranges from 9 to 26%. The results in children were not considered good enough and scarring rates too high to recommend the argon laser for pediatric PWS. The argon laser is rarely used now for PWS.

■ Continuous Wave Dye Laser

It was recognized early on that longer wavelengths of light absorbed by hemoglobin, particularly at 577 nm which coincides with the beta absorption peak of hemoglobin, would be more appropriate for treatment of vascular lesions (Fig. 2.1). An argon laser can be used to energize a rhodamine dye to produce coherent light at 577 or 585 nm. As with the argon laser, the light emerging is continuous but can be mechanically shuttered to produce pulses of light 10s to 100s of milliseconds in duration.

Lanigan et al. (1989) reported the results of treating one hundred patients with PWS with a continuous wave dye laser at 577 nm. A good or excellent response was seen in 63%, with a fair result in 17%; 12% of patients had a poor response. Hypertrophic scarring occurred in 5% and a similar percentage had postinflamma-tory hyperpigmentation. The best results were seen in older patients with purple PWS. These results were similar to those obtained with the argon laser.

Others have also found similar results with argon and continuous wave dye lasers. It is likely that any advantage gained by the longer wavelength of light is offset by the long-pulse durations employed and the use of minimal blanching as an end point. Another study evaluated 28 patients with PWS with the PDL and a continuous wave dye laser delivered through a scanning device. Results were better in 45% of patients treated with the PDL and in 15% of patients treated by the laser with scanner. There was a higher incidence of hyperpigmentation with a continuous wave laser but no differences in the instance of scarring or hypopigmenta-tion.

■ Robotic Scanning Hand Pieces

The major disadvantage of continuous wave lasers in the treatment of PWS is the long-pulse duration resulting in nonspecific thermal damage. In addition, manual movement of a continuous wave laser beam over the skin is dependent on the operator's skill not to under- or overtreat an area. Robotic scanning devices have been developed to try and address some of these difficulties. These hand pieces can be used in conjunction with continuous wave lasers such as the argon laser, and also quasi-continuous systems, such as the copper vapor and potassium titanyl phosphate (KTP) lasers.

Robotic scanning laser devices have been most widely used in the treatment of PWS. The scanner is connected to the laser output by a fiber optic cable. The automated program places pulses of energy in a precise nonadjacent pattern in the shape of a hexagon (Fig. 2.4). The number of pulses delivered will determine the size of the hexagon, which varies from 3 to

Pdl Laser Treatment Pws Leg
Fig. 2.4. Hexagonal clearance of a port wine stain treated with the KTP laser and robotic scanning hand piece (Hexascan) [from S.W. Lanigan (2000) Lasers in Dermatology, Springer Verlag, London]

13 mm in diameter. Adjacent hexagons can then be applied to cover the PWS skin. The advantages of automated scanning devices are shorter pulse durations, uniformity of energy placement, faster treatments, and reduced operator fatigue. In a study using scanning devices compared with conventional techniques the rates of scarring were substantially reduced after scanner-assisted laser treatment. Clinical results were also improved in the scanned patients.

■ Copper Vapor Laser

The copper vapor laser (CVL) is one of two heavy metal vapor lasers used clinically. Results of treating PWS with this laser were reported in the early 1990s. The wavelengths of light emitted by a CVL are 510 and 578 nm. The longer wavelength yellow light is well absorbed by oxyhemoglobin. In contrast to other yellow light lasers, the CVL emits a train of pulses with a duration of 20-25 ns and 10,000-15,000 pulses per second. Because of the very short gap between each pulse of light from the CVL, the biological effect of this laser is similar to that of a continuous wave laser. The CVL is often termed a quasi-continuous laser for this reason.

Good or excellent results have been reported in treating PWS with the CVL. Best results are seen in predominantly purple or red PWS. In comparison with the argon laser, the CVL produced superior results when used with a minimal blanching technique and a laser-associated computerized scanner. In another study (1996), comparing the CVL, argon laser, and frequency doubled Nd:YAG laser, all used with similar pulse widths and a scanner, investigators found only small differences in the results with the three lasers in the treatment of purple PWS. Adverse reactions with the CVL are infrequent, but most studies have been on small numbers of patients. Textural changes and pigmentary disturbances are most commonly reported.

■ Carbon Dioxide Laser

The use of the carbon dioxide laser for treatment of PWS is primarily of historical interest. Yet this laser may still have a role in the removal of hemangiomatous blebs within PWS which are resistant to other lasers. The carbon dioxide laser emits infrared light at 10,600 nm, which is absorbed by tissue water. In a continuous mode the laser will nonselectively vaporize tissue. It is hypothesized that if the majority of ectatic blood vessels are located superficially within the dermis, vaporization of tissue down to this level, but no further, could result in clinical lightening of the PWS without scarring. Prior to the widespread use of the PDL, the carbon dioxide laser was considered of potential value in the treatment of PWS. Lanigan and Cotterill (1990) reported their results using this laser in 51 patients with PWS. Twenty-nine of the patients had failed to respond to argon or continuous wave dye laser treatment. Twenty-two were children with pink PWS. Good or excellent results were seen in 74% of adults and 53% of children. Two children (12%) had a poor result, including a hypertrophic scar on the neck in one child. In another study the tuberous component of 30 patients with PWS was found to be unresponsive to PDL treatment. In all patients the lesions disappeared, but textural changes were seen in 37%, with one patient developing hypertrophic scarring. In view of the excellent safety profile for the PDL in the treatment of PWS, the carbon dioxide laser cannot be recommended as initial treatment of this vascular birthmark.

Currently Available Lasers for Vascular Lesions

Currently the main lasers used for the treatment of vascular lesions including PWS are PDLs and the KTP laser. Recent work has also demonstrated that long-pulsed 755-nm alexandrite and 1064-nm Nd:YAG lasers may be of value in treatment of both PWS, bulky vascular anomalies, and leg vein telangiectasia.

Indications

Lasers currently available for treating vascular disorders have a wide range of applications. Cutaneous ectatic disorders either acquired or congenital can be treated. Particular attention in this chapter will be given to the treatment of PWS, capillary (strawberry) hemangiomas, leg vein telangiectasia (Table 2.2), and facial telangi-ectasia. A number of other disorders of cutaneous vasculature can be treated (Table 2.3). Cutaneous disorders not primarily of vascular origin, e. g., angiolymphoid hyperplasia, adenoma sebaceum, etc., (Table 2.4) can also be treated. Particular emphasis will be given on treating psoriasis, scars, and viral warts in this way.

Table 2.2. Lasers used for treatment of leg vein telangiectasia

Laser

Wavelength

Pulse duration

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