What is PDT?
PDT (Photodynamic thearpy) is a good method for treating multiple Solar Keratosis which are the pre-cancerous red flaky lesions that occur on the backs of hands, face, forehead & other sun exposed aras. PDT may also be used to treat IEC & a variety of other skin conditions, including sebaceous hyperplasia.
The main alternative to PDT for multiple sun spots is efudix cream. The cosmetic results of PDT are generally considered to be the best amongst treatments for Solar Keratosis. Many people find that the treatment leaves their skin looking more youthful.
Conventional PDT is performed at the clinic in two stages on the same day. The first stage of treatment involves an application of PDT Cream in the PDT clinic. The photosensitive chemical in the cream is taken up by abnormal cells (keratinocytes). The second stage of treatment begins around 3 hours later. A specific wavelength of light is focused at an onto the treatment area for 10-15 minutes and this results in destruction of the cancerous and pre-cancerous cells that have taken up the chemical in the cream previously applied.
What types of PDT cream are there?
There are two types of chemical in PDT Cream
- 5-ALA (5-aminolevulinic acid).
- Methyl aminolevulinate (MAL) – in the branded cream Metvix.
There are differences between them with regards to the wavelength of light that is required to activate the cream. The treatment protocols are slightly different. 5-ALA is significantly cheaper but metvix may be less painful and easier to use. It’s fair to say that there is a variety of professional opinion with regards to the differences between 5-ALA & Metvix.
What practical steps are involved with in-clinic PDT?
The process will vary depending on the chemical used, light & condition. Typically, the following steps are involved:
- Scale in the treatment area is gently removed.
- The area is cleaned.
- The PDT cream is applied.
- The light source from the PDT machine is now focused onto the treatment area for 10-15 minutes. Goggles are warn for face treatment.
- After the treatment has finished, you may apply moisturiser. Stay out of strong sun for 2 days afterwards.
- The treatment may be repeated 1-4 weeks later.
What are the side effects of PDT?
- Pain: this may be noticed when the light is applied. There may be discomfort or itching afterwards for a few days.
- Inflammation (redness, swelling) may be noticed afterwards and last a week or so.
- Blistering – unusual.
- An unusual reaction is possible eg. marked redness & swelling that may require an antibiotic.
- Loss of skin pigment – unusual to rare.
What is Daylight PDT?
Up until recently, PDT required in-clinic treatment with the PDT machine to active the cream at a specific wavelength of light.
As the name suggests, daylight PDT involves using daylight instead of the PDT machine to activate the cream. Yes, this sounds good … and is! Metvix is used for both convention & Daylight PDT. The manufacturer of Metvix did a blinded trial and this is what they said: “The study results demonstrated that Daylight PDT is as effective as conventional PDT for treating AK lesions, but with significantly reduced subject pain.”
Daylight PDT is used to treat sun spots on the face and scalp.
You attend the skin cancer clinic to have the PDT cream applied. You then need to go outside within 30 minutes of the cream application, and stay outside for 2 hours. The weather can be sunny or cloudy although treatment can not be completed in rain!
Before starting treatment, any crusty areas should be removed; use salicylic acid or urea cream for a few days beforehand. Use clear sun protection before attending the clinic.
Daylight PDT may have the following advantages over conventional PDT:
- Quicker treatment – no need to come back to the clinic a few hours later for the light application.
- It’s considered less painful than conventional PDT.
How does PDT work?
The chemical (5-ALA or MAL) in the cream is taken up by sun damaged cells called keratinocytes. The non-sun damaged cells don’t take up anything like as much of the chemical. Inside the cells, the chemical is converted to protoporophyrin IX which is a photosensitive substance. Application of specific wavelengths of light (red or sometimes blue) activate the protoporophyrin IX which in turn causes cell destruction.
The chemical is not taken up by cells in the dermis (this is too deep) which is the reason why scarring is very rare and the cosmetic outcome generally excellent. In addition, it seems to have an anti ageing effect on the skin and is often noticed to reduce wrinkles.