What is the photodynamic therapy?
Photodynamic therapy (PDT) is a non-surgical treatment method which is useful to treat certain tumours and precancerous skin conditions, but is also able to produce a considerable rejuvenation of the skin. The principle on which PDT is centred is that of a photodynamic reaction which is able to selectively destroy only some types of cells. The photochemical reaction which is at the base of this method is a photochemical process interposed with light which is designed to absorb the light itself by a photosensitive substance and the subsequent formation of oxygen in its reactive form, which is capable of destroying the cell in which it is formed. In short, the photosensitizer is a molecule which, by acquiring energy from the light, goes into an unstable excited state and liberates energy. The energy liberated in turn goes to excite the oxygen which is present in all cells. When the oxygen molecule is excited by the energy liberated by the photochemical reaction it transforms into its reactive variant (singlet oxygen, superoxide anion and oxygen peroxide), which proves to be toxic for the cell.
Treatment with photodynamic therapy
The photosensitizer for PDT for the skin is 5-aminolevulinico acid (5-ALA), a molecule which is not toxic for man, is small in size, able to penetrate through the skin and is able to select healthy cells from diseased or tumorous cells. In the reaction the 5-ALA is transformed into another substance, ProtoPorphyrin IX (PpIX). The administration of 5-ALA through the skin is therefore able to increase the synthesis of PpIX within the cell. Light acts as the energy which is needed to activate the real active substance that is the PpIX. Numerous light sources are able to activate the photodynamic reaction. Usually, we use red light-emitting diode lamps with a wavelength around 660 nm.
As a general rule there are no particular limitations to the treatment or any special preparation of the skin to be carried out beforehand. There are no limits in age or regarding the presence of accompanying conditions, but it is important that the patient should not be taking potentially photosensitizing medicines. The skin blemishes to be treated often need to be prepared to encourage the penetration of the active substance and therefore if there is any scaling, this needs to be removed in advance. Once the cream containing the photosensitizer is applied to the skin, a dressing is applied as a barrier to encourage the absorption. The dressing is covered to prevent light getting in, as it could activate the treatment, and then we wait for the time needed for the activation (usually a few hours) according to the type of treatment required and/or the type of lesion to be treated. Then the area is exposed to a light source for a variable length of time (usually 15-20 minutes), during which the patient may feel a light warming or burning sensation. The area treated must not be exposed to the sunlight and in the following days there may be an exudative reaction with the formation of small scabs, which will be treated with soothing ointments and antibiotics. 3-4 days after the treatment, the dressing is no longer needed and it remains to wait for the scabs to drop off and the tissue to be completely repaired.
Effects of photodynamic therapy
For superficial lesions, like actinic keratoses, a single treatment is sufficient. For other lesions it may be necessary to repeat the procedure, even without any precise limit. In fact PDT does not cause any damage to the healthy tissues around the lesion.
PDT was created as a specific therapy for precancerous and cancerous lesions of the skin, but it has turned out to also have excellent abilities to improve other conditions. In the case of acne, even in the active phase, it produces a halt in its inflammatory reactivity which is practically immediate and facilitates the use of other methods (peeling) to clean and smooth the skin. Regarding minor degenerative phenomena which are at the basis of non cancerous photoageing, photodynamic therapy exploits the principle by which a cell which is chronically damaged by the sunlight or by UV lamps, unlike a normal one, is able to accumulate, within it, large quantities of photosensitizer. The treatment will therefore prove to be very selective for the damaged cells and is able to improve the signs of photoageing brilliantly. For this reason its use can also be extended to this type of problem with excellent results.