Photodynamic therapy (PDT) is an important tool in dermatologists’ toolbox for actinic keratosis treatment and reduction of nonmelanoma skin cancer risk. Unfortunately, PDT has a bad reputation with patients for being too painful and time consuming. In this high-yield session, Dawn Merritt, DO, discussed practical tips for incorporating PDT into your practice. Dr Merritt briefly reviewed the mechanism of action of PDT before discussing the most common photosensitizers and light sources used in the office. Aminolevulinic acid (ALA) 20% solution and ALA 10% gel are the two photosensitizers available in the United States, with ALA 20% solution approved for blue light use and ALA 10% gel approved for red light use.
Dr Merritt discussed the classic protocol for performing PDT, which includes debridement of lesions, application of the photosensitizer, incubation with or without occlusion, and illumination. Recently, studies have emerged that question the optimal photosensitizer, incubation period, and illumination time. A split-face and scalp study of ALA 10% gel versus ALA 20% solution with a one-hour incubation followed by 1000-second blue-light illumination found that both photosensitizers had similar rates of lesion clearance, while ALA 20% solution was associated with more local skin reactions such as erythema, crusting, and scaling.
Changes in incubation time have led to the development of “painless PDT” in recent years. Dr Merritt reviewed a small, split-face study of 23 patients comparing conventional blue light PDT with one-hour incubation and 1000-second illumination with no incubation and illumination for 30, 45, or 60 minutes. All patients who received immediate illumination experienced significantly less pain, and lesion clearance was similar between the two protocols. Dr Merritt cautioned that there is no consensus on which sensitizer, illumination source, or illumination time is preferred, but all studies have shown noninferiority with conventional PDT. Dr Merritt has performed this “painless PDT” with red light using a 30-minute illumination time and seen good lesion clearance with low rate of adverse events. Dr Merritt does recommend using occlusion for PDT on the upper extremities for higher efficacy. To conclude, Dr Merritt discussed case studies of newer uses for PDT including acne vulgaris, photorejuvenation, and folliculitis decalvans.