Correlation between treatment time, photobleaching, inflammation and pain after photodynamic therapy with methyl aminolevulinate on tape-stripped skin in healthy volunteers

Photodynamic therapy (PDT) is an attractive treatment option for skin diseases such as actinic keratosis, since large skin areas can be treated with high response rates and good cosmetic outcomes. Nevertheless inflammation and pain are still major side effects. The aim of this study was to investigate the extent to which less time-consuming PDT treatment regimens using methyl aminolevulinate (MAL) decrease protoporphyrin IX (PpIX) photobleaching, inflammation and pain. Twenty-four healthy volunteers were treated with 4 different interventions on each forearm. All 8 fields were tape-stripped 10 times. On the right arm MAL was applied for 20, 40, 60 or 180 min, followed by further incubation after wiping off MAL until 180 min after start and then illuminating with red light 180 min after start. On the left arm MAL or vehicle was applied for 30, 60, or 90 min and illuminated immediately after MAL removal. PpIX fluorescence, photobleaching, objective and subjective erythema (as a measure for inflammation), pigmentation and pain were measured. The results showed a significant correlation between incubation time, time until illumination and photobleaching. Furthermore, there was a significant correlation between photobleaching and erythema and also between photobleaching and pain. In conclusion, shorter PDT regimens result in decreased photobleaching and also less inflammation and pain. We hypothesize that a shorter incubation time is important for the optimal specific subcellular distribution of PpIX and to avoid unspecific distribution. We propose a shorter PDT regimen, "Pulse PDT", comprising, for example 30 min incubation with MAL and illumination after 180 min, and we have planned a study of actinic keratosis and "Pulse PDT".