The relation between methyl aminolevulinate concentration and inflammation after photodynamic therapy in healthy volunteers.

Inflammation and pain are well known adverse-effects in photodynamic therapy (PDT). There is currently a tendency towards introducing lower concentrations of the photosensitizer than used in the standard treatment for various indications. The aim of this study was to investigate whether reduced concentrations of methyl aminolevulinate (MAL) can reduce inflammation (erythema) during PDT treatment. We measured the formation of protoporphyrin IX (PpIX) using fluorescence and monitored both erythema and pain during and after PDT treatment with conventional 16% MAL and threee reduced concentrations of 2, 0.75, and 0.25% in twenty-four healthy volunteers. We found that lowering the MAL concentration reduced PpIX fluorescence and erythema after PDT treatment. There was a strong correlation (R(2) = 0.70) between the PpIX fluorescence and erythema after treatment. A further increase in erythema after PDT was dependent on pre-treatment skin erythema. PpIX fluorescence could explain 70% of the increase in erythema (P < 0.0005). Pain and post-treatment hyperpigmentation can be reduced but not eliminated by limiting the MAL concentration. An efficacy study of PDT with these three reduced concentrations has not been performed.