Photodynamic therapy of recalcitrant warts with 5-aminolevulinic acid: a retrospective analysis.

Sir, Photodynamic therapy (PDT) with topical application of 5aminolevulinic acid (ALA) has been successful in the treatment of super®cial non-melanoma skin tumours (1). When applied topically to the skin, ALA is absorbed into the epidermal cells and biosynthesized to the light-sensitive metabolite photoporphyrin IX (PpIX). When cells with accumulated PpIX are exposed to light of certain wavelengths, free radicals are released as singlet oxygen, leading to cell death (2). Recently it has been reported that ALA-PDT also has antiviral properties (3). Selective production of PpIX has been demonstrated by ̄uorescence measurements after ALA application to genital warts, indicating a speci®c af®nity for ALA in human papilloma virus infected tissue (4). A preliminary study showed that repetitive treatment with ALA and white light has a curative effect on recalcitrant verrucae (5). Encouraged by these results, we treated patients who were referred to our department with warts resistant to other treatments, with ALA-PDT.