Photodynamic therapy represents a comparatively gentle and at the same time effective treatment procedure for superficial skin tumors. With the help of so-called photosensitizers and light waves, substances are released in the organism that specifically lead to cell death of the diseased cells.
What is photodynamic therapy?
Photodynamic therapy represents a comparatively gentle yet effective treatment procedure in dermatology for superficial skin tumors. Photodynamic therapy (PDT) is a diagnostic and noninvasive therapeutic procedure used in the treatment of superficial skin tumors (carcinoma in situ). The procedure is an effective and gentle alternative to conventional invasive surgical procedures. Thus, photodynamic therapy generally leads to better cosmetic-aesthetic results with significantly less to no scarring. Characteristic disease patterns associated with photodynamically treatable tumors are Bowen’s disease, actinic keratoses, and basal cell carcinoma (semimalignant skin tumor), which is the most frequently diagnosed type of skin tumor in Central Europe. In addition, viral skin lesions (including warts) and wet forms of age-related macular degeneration (AMD) can be effectively treated by photodynamic therapy to obliterate abnormal blood vessels in the center of the retina.
Function, effect, and goals
Photodynamic therapy is used primarily for superficial skin tumors (eg, basal cell carcinomas) that have penetrated less than 3 mm into the skin and may occur in the setting of actinic keratoses or Bowen’s disease, among other conditions. In addition, viral changes of the skin (e.g. warts) can be effectively treated by the procedure. For this purpose, a special cream is applied topically to the affected skin area and covered light-proof for about 3 hours with the help of an adhesive plaster. The light sensitizer contained in the cream (e.g. Metvix, 5-ALA or delta-aminolevulinic acid) selectively stimulates the pathologically altered skin cells to synthesize protoporphyrin IX, which is a precursor of the organism’s own porphyrin. Porphyrin, in turn, is photoactive and, under the influence of certain light waves, stimulates the biosynthesis of aggressive oxygen radicals (so-called photodynamic effect), which cause the cell death of the abnormal cells. For the most part, this chemical reaction has no effect on the healthy cells. Since pain may be experienced to varying degrees by individuals during irradiation, a pain-relieving medication is administered before the therapy begins and the skin area to be treated is cooled during the procedure with the aid of a cold air device. Following the treatment, the irradiated skin areas should be cooled and oily creams or ointments should be avoided. An antibiotic gel may be applied to soothe and relieve pain. Depending on the extent and stage of the skin tumor, the therapy may have to be repeated. For example, in the case of a pronounced actinic keratosis, a repetition of the photodynamic therapy is indicated after about 4 weeks. Furthermore, six-monthly check-ups are recommended for early diagnosis of recurrences. The photodynamic effect described above can also be used for diagnostic purposes (photodynamic diagnostics or fluorescence diagnostics). After the affected skin areas have been treated with the photosensitizer, a Wood lamp (black light) can be used to visualize the porphyrin selectively enriched in the pathologically altered cells. This allows early diagnosis and detailed identification and assessment of the diseased areas of skin, which is particularly important in the often scattered forms of actinic keratosis. For some time now, photodynamic therapy has also been used for wet forms of age-related macular degeneration. Hereby the light-sensitive dye (among others Verteporfin) is infused into the arm vein in the run-up to the laser treatment. The subsequent irradiation with light waves can specifically obliterate the damaged blood vessels in the eye that have accumulated the photosensitizer. Following photodynamic therapy, there is usually an increased sensitivity to light, which makes it necessary to wear dark sunglasses and appropriately protective clothing.
Risks, side effects and dangers
In general, photodynamic therapy is associated with only minor risks and side effects. As a rule, after the treatment, some redness and sunburn-like skin irritations can be observed in the area of the treated skin. These usually disappear within a few days. In rare cases, crust formation, weeping skin areas and swelling can also be observed following photodynamic therapy. Skin crusting, like scabs, usually disappears on its own after a few days. In extremely rare cases, photodynamic therapy will cause a pigmentary shift (postinflammatory hyperpigmentation), which is manifested by excessive pigmentation (dark discoloration) of the skin. As part of the treatment of age-related macular degeneration, the procedure can cause edema (fluid accumulation) and further damage to the retina. In addition, worsening of visual acuity or blindness as a result of photodynamic therapy cannot be ruled out.
