Laser-mediated photodynamic therapy

Photodynamic therapy (PDT) has evolved since its inception at the beginning of the 20th century, when it was defined as an oxygen-dependent reaction between a photosensitizing dye and light. Photosensitizers and light sources have since been continually optimized for distinct applications and tissues. Systemic porphyrins, such as hematoporphyrin, were the first photosensitizers to be used, mostly to treat tumors. The first light sources used were broad-band, noncoherent lights, such as quartz, xenon, tungsten, or halogen lamps. The wavelengths of light chosen were based upon the absorption spectrum of porphyrins: blue because the largest peak is at 400 nm (the Soret band) and red because of its greater penetration depth but lesser absorption at 650 nm (a Q band). Systemic photosensitizers caused prolonged photosensitivity, and broad-band light sources had limitations and side effects. The development of topical photosensitizers, such as 5-aminolevulinic acid, and the advent of lasers in recent years have advanced PDT for cutaneous use. In the 1990s, red lasers were applied to PDT because of their increased skin penetration despite lesser absorption by porphyrins. Broad-band blue light and red light have been studied extensively, the former achieving Food and Drug Administration approval in combination with topical aminolevulinic acid for the treatment of actinic keratosis in 1997. These lasers and light sources caused significant side effects, such as discomfort, erythema, crusting, blistering, and dyspigmentation. The recent application of the long-pulsed pulsed dye laser (595 nm) after topical aminolevulinic acid greatly minimized side effects without compromising efficacy. Long-pulsed pulsed dye laser-mediated PDT has since been shown to be effective in treatment of actinic keratosis, actinic cheilitis, sebaceous hyperplasia, lichen sclerosus, and, most recently, acne vulgaris. Finally, intense pulsed light sources have been introduced to PDT for the treatment of photodamage and acne, offering advantages of versatility in wavelengths and applications.