Short-term chemical pretreatment cannot replace curettage in photodynamic therapy

BACKGROUND: Guidelines for photodynamic therapy (PDT) recommend pretreatment with curettage/debulking to enhance intracellular formation of protoporphyrin IX (PpIX). However, studies suggest that new chemical pretreatment procedures may replace curettage/debulking.

PURPOSE: To investigate how pretreatment with curettage and two combination ointments containing calcipotriol/betamethasone and salicylic acid/betamethasone affect PpIX fluorescence after the application of methyl aminolevulinate MAL and 5-aminolevulinic acid (BF-200 ALA).

METHODS: Four fields on the forearms of 30 healthy volunteers were pretreated with curettage or short-term application of calcipotriol/betamethasone or salicylic acid/betamethasone for 20 min. Two fields were not pretreated, thus serving as reference. After pretreatment, MAL or BF-200 ALA was applied for 24 h, and PpIX fluorescence was measured hourly from 1 to 5 h and after 18, 21 and 24 h.

RESULTS: Curettage significantly enhanced PpIX fluorescence for MAL from 1 to 21 h (P < 0.0041). For BF-200 ALA, curettage enhanced fluorescence from 1 to 5 h (P < 0.000064), while fluorescence was lower from 18 to 24 h. Pretreatment with salicylic acid/betamethasone and calcipotriol/betamethasone before BF-200 ALA application did not increase PpIX fluorescence from 1 to 5 h compared to no pretreatment, and both were significantly inferior to curettage (P < 0.0017 and 0.0024, respectively).

CONCLUSION: Curettage significantly enhances PpIX fluorescence from 1 to 5 h and is superior to short-term chemical pretreatment. Our results support curettage as standard pretreatment in PDT.