An investigation of the fluorescence induced by topical application of 5-aminolaevulinic acid and methyl aminolaevulinate at different body sites on normal human skin.

BACKGROUND

Although discovered over a century ago it is only in the last 25 years that photodynamic therapy (PDT) has been the focus of intense research. This versatile treatment modality has been shown to be effective in treating a wide variety of malignancies, and with the increasing incidence of non-melanoma skin cancer (NMSC) is a recognised treatment in dermatology clinics worldwide. There is little known as to whether different body sites influence the uptake and conversion of 5-aminolaevulinic acid (ALA) or methyl aminolaevulinate (MAL) to protoporphyrin IX (PpIX). In this study we investigated the characteristics of PpIX fluorescence within normal skin following the application of both ALA and MAL to four different body sites and the effect of tape stripping.

METHODS

A total of 17 healthy volunteers were recruited, and both ALA and MAL were applied to the inner forearm, outer forearm, lower leg and back for 4h. PpIX fluorescence was detected using a non-invasive spectroscopy system.

RESULTS AND CONCLUSIONS

PpIX fluorescence (following the application of either ALA or MAL) does vary significantly at different body sites with the lower leg producing the least. Following the application of ALA, peak fluorescence was noted at all body sites at 24h, except the lower leg, which peaked at 7h. In contrast MAL induced fluorescence at all body sites, peaked earlier at 7h and had significantly decreased by 24h. Removal of the stratum corneum by tape stripping was also shown to significantly increase PpIX fluorescence but did not alter the time course.