Background: Most clinical studies using photodynamic therapy (PDT) with topical application of delta-aminolaevulinic acid (delta-ALA) use red light because it allows greater depth of penetration. However, given the porphyrin-like spectrum of delta-ALA-induced photosensitivity, violet light provides a maximal overlap with the excitation spectrum of protoporphyrin IX, meaning that PDT with violet light uses less light energy to induce the phototoxic reaction.
Aim: To study the efficacy of violet light in combination with topical delta-ALA PDT in the treatment of pre-malignant and malignant skin lesions.
Methods: Eight hours after 20% delta-ALA was applied topically, photoirradiation was performed with an incoherent light source (Philips HPM-10, 400 W) emitting predominantly violet light (400-450 nm). Lesions received 10-20 J/cm2 during an exposure time of 30 min. The 38 subjects treated included three with basal cell naevus syndrome with multiple (> 30) superficial and nodular basal cell carcinomas (BCCs), one subject had multiple lesions of Bowen's disease, involving 50% of the scalp, and the remaining 34 subjects presented a total of 35 superficial BCCs, 10 nodular BCCs, four large solar keratoses and five solitary lesions of Bowen's disease.
Results: Complete remission both clinically and histologically was seen after a single treatment in 82% of the superficial BCCs (100% after a second treatment), 50% of the nodular BCCs, one of the four solar keratosis lesions (partial remission in the other three) and 90-100% of the solitary lesions of Bowen's disease.
Conclusions: delta-ALA PDT using violet light appears to be a well tolerated and effective alternative treatment for premalignant and malignant skin lesions, especially when there are multiple lesions or large patches comprising a large area of skin.