What is PDT?
PDT (Photodynamic therapy) PDT is a a very method for treating multiple Solar Keratosis which are 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.
PDT requires a visit to a clinic. The cream is stored in a monitored vaccination fridge, and is applied by the practitioner to affected areas. The photosensitive chemical in the cream is taken up by abnormal cells (keratinocytes). The cream only becomes active when the skin is exposed a special light (conventional PDT) or by daylight (daylight PDT).
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. The main alternative to PDT for multiple sun spots is efudix cream.
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 is Daylight PDT?
Up until recently, PDT required in-clinic treatment with a special light to active the cream at a specific wavelength of light.
The good news is that daylight may also be used to activate the cream. Daylight PDT is used to treat sun spots on the face and scalp. Daylight PDT is somewhat of a breakthrough in the treatment of Sun Spots. However, daylight PDT is not used for skin cancer treatment.
Evidence from a number of randomised trials show that Daylight PDT is as effective as conventional PDT for treating AK lesions but with significantly reduced subject pain. It is cheaper than conventional PDT because there is less time required at the clinic.
The practicalities are that you attend the skin cancer clinic to have the Metvix® cream applied. You then go outside within 30 minutes of the cream application. You must stay outside for 2 hours. The weather can be sunny or cloudy.
You may be advised to use 5% salicylic acid cream, or urea cream, for a few days before treatment.
A ‘chemical’ sunscreen will need to be applied at least 15 minutes before application of the metvix. A side-effect of Metvix® is a sunburn-like inflammation, so you won’t want to add sunburn to sunburn. Do not use a ‘physical’ (reflective) sunsreen like the zinc-containing ones that cricketers use on their nose, or the metvix won’t work. Use a chemical suncreen instead. Metvix® is activated by sunlight rather than UV light. A chemical sunscreen just stops The UV light and not daylight that activates the Metvix®.
Crusty areas area removed at the clinic just prior to application of the cream.
It is sensible to use a moisturiser for a week after the treatment.
What should I do after daylight PDT?
The following protocol follows the Australian daylight PDT expert consensus guideline.
- Go outdoors within 30 minutes of leaving the clinic
- Stay outdoors for 2 hours. Do not cut this short, but do not prolong the time either.
- On an uncomfortably hot day, you make take shelter from time to time in a shaded outdoor area.
- Avoid water-based activities or activities that may result in excessive perspiration.
- Avoid darkly shaded areas (e.g. those close to a building or at the back of a balcony or deck) where there is a lack of diffuse light.
- Ensure that the treatment area is continuously exposed to daylight (e.g. by not wearing a scarf or hat if the affected area is on the scalp).
- What if it rains? Take shelter from the rain in an undercover outdoor area with diffuse light and completes the 2-h exposure to daylight.
Get a checkup 3 months after the treatment.
What are the practical steps with conventional PDT?
Conventional PDT uses a special type of lamp and is a little more involved than daylight PDT.
The process will vary depending on the chemical used, light & condition.
Typically, the following steps are involved:
- The skin is prepared as for daylight PDT, and the PDT cream is applied.
- The light source from the PDT machine is applied around 3 hours later 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 conventional PDT?
- Pain: this mainly an issue with conventional PDT. Pain 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 is unusual.
- An unusual reaction is possible eg. marked redness & swelling that may require an antibiotic.
- Loss of skin pigment is a complication.
Daylight PDT has fewer side effects than conventional PDT. Mild scaling and a sunburnt appearance peaks at 3 days and resolves within 7 days.
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.