Basic and Clinical Studies of Laser for Hyperpigmented Skin Lesions

Abstract

It is of vital importance for laser therapy in hyperpigmented skin lesions to find optimum conditions with respect to wavelength, energy density, pulse width, treatment interval, treatment method (for example, the 1st irradiation immediately followed by the second), etc. In this study we irradiated dye laser (585nm), ruby laser (694.3nm), alexandrite laser (750nm) and Nd-glass laser (1060nm) to the skin of spotted black guinea pigs and hyperpigmented human skin lesions to study whether differences in the wavelength of pulse laser may affect therapeutic results or not. Consequently, it was found that rudy laser and alexandrite laser were effective against skin lesions due to melanin particle deposition and Nd-glass laser against tattoos. The pulse width dependence was discussed between 0.15-2msec. using rudy laser. Melanin particles deposited in the basal layer were more selectively destructed by the shorter pulse laser.
When the energy density was increased above a certain threshold value, non-selective damage of tissues occurred. Since selectivity is one of the important features of laser therapy, an inadequately high energy irradiation is considered useless. In the meantime, we investigated retrospectively 645 patients who underwent ruby laser treatment at our hospital and could be followed up for more than 6 months during the last decade. The treatment was effective for 45% of patients with congenital nevus spilus. The effective rates were 94%, 50%, 80%, 59%, 69%, 22% and 38% in the groups with acquired nevus spilus (Becker), nevus cell nevus, epidermal nevus, nevus pigmentosus senilis, seborrheic keratosis, cafe-au-lait spots and Ota's, respectively. Nevus cell nevus involving the surroundings of the eyelid, palm, sole and lip could be more effectively treated, with a high effective rate of 84%. In the treatment of superficial hyperpigmented skin lesions, rudy laser with 450μsec. and 15J/cm² was less effective than the conventional ruby laser with a longer pulse width. To sum up, short pulse laser in the visible region, is thought to be suitable for the treatment of superficial hyperpigmented skin lesions, short pulse rudy laser or alexandrite laser for deep melanin particle deposition, and short pulse Nd-glass laser for tattoos in Japanese patients, respectively.