Background: Findings of in vitro studies have demonstrated that dermatophytes and yeasts can be effectively photosensitized after topical delivery of 5-aminolevulinic acid (ALA). This procedure, called photodynamic therapy (PDT), seems to lack mutagenic activity and hazard of selection of drug-resistant strains.
Methods: Twenty percent ALA preparation in Eucerin cream was applied under an occlusive dressing to skin lesions of nine patients with clinical and microbiological evidence of interdigital mycosis of the feet. After 4 h, lesions were irradiated with 75 J/cm(2) of broad-band red light. Interdigital lesions of the other foot served as control (treated with only light or only ALA). After 7 days from the first treatment, no further treatment was delivered if lesions were not clinically evident and direct microscopic examination was negative. Otherwise, three additional weekly treatments were delivered. Four weeks after the last treatment, patients had a final follow-up clinical and laboratory examination.
Results: Clinical and microbiological recovery was seen in six out of nine patients after one (four cases) or four (two cases) treatments. However, after 4 weeks, recurrences were seen in four patients. Overall tolerability was always good.
Conclusion: Under the conditions employed in the present study, ALA-PDT had good therapeutic effects on interdigital mycosis of the feet. However, recurrences were quick. In vivo environmental conditions, i.e. temperature, humidity and pH of the interdigital skin, could induce a poor cell uptake of ALA and a deficient biosynthesis of photosensitizing protoporphyrin IX. In addition, the irregular tridimensional shape of this peculiar anatomical area could lead to a non-uniform delivery of light and/or ALA cream. However, the present results can stimulate further studies on the PDT of superficial skin mycoses.