Either hypo- (lightening) or hyper – (darkening) pigmentation have been reported to occur in subjects treated with lasers. Regrettably, the rigorous determination of pigmentary changes has not been documented. The pigmentary changes seen with laser treatment are generally transient, although the appearance/disappearance period can be from days to months. The clinical perception is that pigmentary changes, hyper – or hypo-, are a consequence of postinflammatory reaction or loss of melanocytes, respectively, and are more common in darker-skinned individuals. In any case, the precise reason(s) is unclear.
Lanigan [120] reported the incidence of hyperpigmentation to be 2% in a multicenter, prospective study of 480 subjects receiving 3143 laser hair-removal procedures. In general, the incidence of hyperpigmentation associated with permanent hair removal is greater for short wavelength lasers used in dark-skinned subjects [121]. For example, treatment with a ruby laser had a 1% incidence of hyperpigmentation in Fitzpatrick skin types II/III, and nearly 10% in skin types IV-VI [117]. This may have more to do with the selection of laser, than the true hyperpigmentation observed in these patients. In a prospective clinical study evaluating the effect of a 595 nm dye pulsed laser to treat port wine stains in Japanese subjects, hyperpigmentation up to 17% was reported [122]. The response was mild and transient in this study. In a study of the effect of a short-pulse erbium:YAG laser on acquired melanocytic nevi, postinflammatory hyperpigmentation was reported in 2 out of 14 patients [123]. In a study of 87 Korean patients with Ota’s nevus treated with Q-switched alexandrite laser, 14 subjects had hyperpigmentation [124]. Rogachefsky et al. [125] evaluated hair removal using a diode laser (810 nm) using long pulse durations of 200-1000 msec. delivering fluences of 23-115 J/cm2. In five suntanned individuals, hyperpigmentation and hypopigmentation were reported at six months following treatment, primarily at the sites receiving the highest fluence (115 J/cm2). These examples, and others (Table 23.2) provide evidence of hyperpigmentation associated with the use of different lasers for nonablative
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Table 23.2 Examples of Studies Reporting Pigmentary Change Following Laser Treatment
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treatment of pigmentary/vascular lesions and permanent hair removal [126-128]. The conclusion is that short wavelength long-pulse in darker-skin types is associated with transient hyperpigmentation following laser treatment.
In the Lanigan study [120], the incidence of hypopigmentation was 1.2%. Kono et al. reported no hypopigmentation in a study of 18 Asians treated with a Q-switched ruby or long-pulsed 595 nm laser for facial lentigines [113]. In a prospective study of 322 subjects undergoing 3 or more permanent hair-removal treatments with a long-pulsed alexandrite laser, 2 cases of hypopigmentation were reported [21]. In the studies where hyperpigmentation [116-120] was noted, hypopigmentation was also reported with a similar incidence and severity. On the other hand, Moreno-Arias [129] indicated that long-term hypopigmentation is extremely rare. Specifically, in a 5-year retrospective analysis involving over 15,000 administered treatments for laser hair removal, only one case of hypopigmentation was noted. As with hyperpigmentation, the mechanism of laser-induced hypopigmentation is unknown. One hypothesis is that melanocytes at the epidermal/dermal junction are destroyed, leading to skin lightening.