NEW YORK – For treating actinic keratoses appearing over large or disseminated surface areas, daylight is often a better strategy than artificial light is for activating photodynamic therapy (PDT), according to an update on strategies at the summer meeting of the American Academy of Dermatology.
The evidence that daylight is at least as effective as artificial light for grade 1 and 2 actinic keratoses has created a “really exciting new opportunity” for those with disseminated disease, according to Dr. Emily J. Fisher, director of Mohs surgery at Mercy Health Physicians, Cincinnati, Ohio. This approach is not only a more efficient way to treat large or multiple areas of skin, but it is better tolerated, further facilitating treatment of bigger surface areas.
Moreover, for physicians not currently equipped with blue or red artificial light, daylight activation “is a great way to incorporate PDT into your practice,” Dr. Fisher added. She suggested that PDT, which has been associated with clearance rates exceeding 70% with a single treatment in many studies, appears to be at least as effective as the topical treatments that are employed more often, such as 5-fluorouracil (5-FU) or imiquimod.
When comparing efficacy across studies, “PDT seems to have a higher response than [does] our topical treatments,” but Dr. Fisher cautioned that there are no high-quality, head-to-head comparisons, so there is no definitive evidence of the superiority of one over the other.
However, in patients with multiple actinic keratoses spread over a substantial area of the skin or who have lesions in more than one anatomical site, daylight PDT is a practical approach now widely used in Europe and several other parts of the world, according to Dr. Fisher. She reported that five randomized trials have demonstrated that daylight PDT is effective.
Most aspects of daylight PDT are the same as conventional PDT, according to Dr. Fisher. The skin is first prepared by removing scales and crusts to improve penetration of the photodynamic agent, whether aminolevulinate acid (ALA) or methyl aminolevulinate (MAL). Prior to light exposure, the occlusion time with the photodynamic agent is the same 3 hours. Also, light exposure in both cases should begin within 30 minutes, which may be a consideration for those depending on daylight.
“Patients really should not go indoors or into shade for more than 5 minutes at a time,” Dr. Fisher reported. The problem is that the activity of the intracellular photosensitizing chemicals can build up without light exposure, producing pain and reducing the tolerability of the treatment.
Consensus guidelines have been published for daylight PDT in Australia (J Eur Acad Dermatol Venereol. 2012 Jun;26:673-9.). According to Dr. Fisher, the guidelines recommend a light intensity of greater than 130 W/m2, which is a dose provided by sunlight within the continental United States but not at distant points from the equator, such as Alaska. The guidelines also specify that sun exposure take place with a minimum temperature of 10° C. Dr. Fisher said that activity is diminished at lower temperatures.
“After 2 hours of exposure, patients should wash off the ALA and avoid further exposure for about 48 hours,” said Dr. Fisher, who recommended chemical sunscreens on areas of the skin not being treated.
“I think that over the next few years, this is going to have a big place in patient treatment. It is more convenient and better tolerated,” Dr. Fisher reported. She said that several modifications with the potential to enhance efficacy, such as pretreatment with retinoids or employing 5-FU after PDT, are strategies that have shown promise in small studies and may prove to be helpful through expanded clinical investigation.