The monitoring of ALA-induced protoporphyrin IX accumulation and clearancein patients with skin lesions by in vivo surface-detected fluorescence spectroscopy

The method of surface-detected fluorescence has been used to monitor the em ission intensity from 5-aminolaevulinic acid (ALA)-induced protoporphyrin I X (PpIX) in lesions and corresponding adjacent normal skin. Three types of lesions were examined: psoriatic plaques, actinic keratosis and basal cell carcinoma. This study included a total of 14 human volunteers on whom ALA-i nduced PpIX formation and clearance was monitored for a total of 48 h post- ALA application. Both an ALA dose-ranging study, as well as a comparison of results between normal and lesional tissue at a fixed ALA dose, were carri ed out. For the dose range examined (10-30%), there was no ALA dose depende ncy of the PpIX fluorescence for any of the lesions tested. Although all th ree lesions tested did show enhanced PpIX fluorescence as compared with nor mal skin, there was considerable lesion-to-lesion variability. Thick psoria tic plaques seem to give longer PpIX retention times than those of thin les ions. Limitations of the surface-detected fluorescence methodology are disc ussed.