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Editorial |

Photodynamic Therapy in Daylight for Actinic Keratoses

Hans Christian Wulf, MD, DMSc, PharmD1
[+] Author Affiliations
1Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Denmark
JAMA Dermatol. 2016;152(6):631-632. doi:10.1001/jamadermatol.2015.5979.
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In conventional photodynamic therapy (PDT) for the treatment of actinic keratoses (AK), 5-aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) is applied to the skin after gentle curettage and stays there for a defined period of time (often 3 hours) to ensure accumulation of protoporphyrin IX (PpIX).1 During this time the treated area must be covered against light by a bandage. After the PpIX accumulation, certified lamps are used for a short illumination of the photosensitized skin to activate PpIX.2,3 In this process PpIX loses its activity and fluorescence property. The emission spectrum of the lamps must cover wavelengths that are absorbed by PpIX to a high degree, and absorbed by other skin components to a low degree. This is done to ensure skin penetration, especially when treating thicker lesions. The absorption peaks of PpIX are found around 412, 509, 544, 582, and 635 nm, mainly in the blue, green, and red parts of the spectrum.4 Conventional PDT is often associated with pain and inflammation, and PDT with daylight as the activating light source, “daylight PDT,” was invented to overcome some of these problems.5

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PpIX Fluorescence Increase in Conventional PDT and Daylight PDT

The upper curve illustrates protoporphyrin IX (PpIX) in skin covered from light and the lower curve illustrates a small PpIX formation half an hour after methyl aminolevulinate (MAL) application and no accumulation at all during the following 2 hours of daylight photodynamic therapy (PDT). AU indicates arbitrary units; pdt, photodynamic therapy; PpIX, protoporphyrin IX.

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