Photodynamic therapy (PDT) is a clinically approved, minimally invasive therapeutic procedure that can exert a selective cytotoxic activity toward malignant cells. The procedure involves administration of a photosensitizing agent followed by irradiation at a wavelength corresponding to an absorbance band of the sensitizer.
How does photodynamic therapy work?
PDT works by direct injury to the target cells and tissues. This involves the production of an activated oxygen molecule that can injure or destroy nearby cells. Because the normal skin barrier is not present at the sites of the actinic keratoses, photosensitizing molecule is preferentially absorbed there and then activated by light. The activated oxygen destroys the adjacent abnormal tissue. Once the areas have healed following PDT, the areas are reexamined to see if additional treatments or biopsies are needed.
With traditional cryosurgery (freezing with liquid nitrogen), only the visible actinic keratoses can be treated. Since many actinic keratoses are often not evident, PDT might be preferable since it presumably would destroy these “subclinical” lesions. PDT allows for treatment of an entire area of sun damage simultaneously, but subsequent treatments may be necessary.
How is PDT used to treat the skin?
PDT using Levulan and a proprietary blue light is currently FDA approved for the treatment of early skin precancers called actinic keratoses (rough scaly spots generally on sun-exposed skin). PDT is also known as “ALA/PDT treatment” or “Super Blue Light.” It has been referred to as a “super photo facial” when the photosensitizer is used with a machine called intense pulsed light or IPL. These treatments may help remove sun-damaged precancerous skin. Sun damage, fine lines, and blotchy pigmentation may also be improved because of the positive effect of PDT. PDT seems to reduce oil gland function and so is helpful in treating acne and rosacea.