non-oncologic applications of photodynamic therapy in dermatology

Topical photodynamic therapy is a two-step technique that requires the presence of a photosensitizer, photoactive wavelengths of light, and oxygen for the treatment of malignant or benign diseases. When light is absorbed by the photosensitizer, it leads to its activation with transfer of its energy to molecular oxygen, generating reactive oxygen species that destruct target cell by direct cytotoxicity An ideal photosensitizer should have the capability of localizing specifically in neoplastic tissue in short time, have a short half-life and rapid clearance from normal tissues and should be activated at wavelengths with optimal tissue penetration. Photosensitizers can be categorized by direct chemical structure into several broad families; Porphyrin platform, Chlorophyll platform and Dyes. The most commonly used photosensitizers in dermatology are the topical 5-ALA and its methyl ester Methyl aminolevulinate Topical ALA and its derivatives posses several advantages. The time between their administration and light delivery is short (3-4 hours) compared with other photosensitizers. The treatment itself is very simple, convenient with excellent cosmetic results and no systemic photosensitization. Lastly the treatments can be repeated without any limitation and with no cumulative effects. The ideal light source in cutaneous PDT should be well absorbed by the photosensitizer, achieve a desirable penetration depth to reach target and be of adequate fluence and duration to drive PDT reaction. Light sources available for PDT include; broadband lamps, lasers, intense pulsed light and diode lamps.