Photodynamic Therapy (PDT) for superficial skin lesions.
This page has been written to help you understand more about Metvix Photodynamic therapy. It tells you what it is, how it works, how it is used to treat skin conditions, and where you can find out more about it. For further information contact your accredited Skin Cancer Doctors at Skin on Forty-Five for advice or to review of any lesions of concern.
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What is photodynamic therapy?
Photodynamic therapy (PDT) is a technique that is used to treat certain types of skin cancers such as superficial Basal Cell Carcinoma and areas of sun-damaged skin (Actinic Keratosis) that might become cancer in the future. In PDT, a cream (Metvix) is applied to the area to be treated which is activated by light selectively killing the abnormal cells in the skin.
How does photodynamic therapy work?
PDT uses a light-sensitive chemical called a photosensitiser in a cream called Metvix. This photosensitiser is not active when it is applied to the skin without light. However, when red light or daylight then shines onto the skin where the photosensitiser was applied, the photosensitiser is activated. This activates the photosensitizing agent which is selectively absorbed into the abnormal cells, destroying the cancer cells. After the inflammatory reaction clears, the sun-damaged skin will either be cured or improve.
What skin conditions can be treated with photodynamic therapy?
PDT can be used to treat various superficial skin conditions including:
Actinic (solar) keratoses – early sun-damage, a pre-cancer; or a whole area of sun-damage (field change or “field cancerisation”).
Superficial Basal Cell Carcinoma
Bowen’s disease (in situ squamous cell carcinoma), a pre-cancer.
What does the Daylight PDT protocol involve?
MAL-PDT using natural daylight has the benefit of being less painful whilst being equally effective. Treatment can be undertaken during spring, summer or autumn in Taranaki.
The natural daylight PDT procedure is as follows:
- To improve efficacy, patients can be using a peeling cream for 10 days or so prior to treatment (eg urea cream).
- A suitable day is selected for treatment; overcast with temperature over 10C is best. In most parts of the world, treatment can be undertaken year-round during office hours. Rainy days are unsuitable.
- The skin to be treated is gently washed.
- A clear sunscreen is applied to all skin to be exposed to daylight including intended treatment area (it can also be applied after the treatment cream)
- The field to be treated is marked out
- Scale and crust are lightly scraped off
- Methyl aminolevulinate cream is applied to the field. One to two grams (one tube) will treat the entire face.
- No more than half an hour later, the patient should go outdoors to expose the treated area to daylight. Delay in exposure leads to greater pain.
- If it is sunny during summer, stay in a lightly shaded area. If it starts to rain, move to an outdoor shelter exposed on 3 sides.
- Sit quietly during the session, rather than taking exercise, as sweat will reduce the penetration of the medication.
- Two hours later, the cream is washed off using saline.
- Remain indoors for the rest of the day. If it is essential to be outdoors, reapply broad-spectrum sunscreen and/or cover-up.
Natural daylight PDT is followed by sunburn-like inflammation in treated areas for 5 to 8 days. The skin is red, and may become blistered and crusted. The reaction tends to be most severe at 3 to 4 days after treatment. Redness can be reduced by pre-treatment with topical steroid.
What can you expect following treatment?
The treatment area typically becomes red and swollen. Moderate to severe stinging, and/or a burning sensation at the
time of treatment is common. The sensation is similar to that of a bad sunburn. The first 24-48 hours are the worst, so allow for down-time from work and other activities during this period. Formation of blisters and pustules are less common. Mild to severe flaking/peeling of the skin follows, this usually subsides in 7-10 days. Reactions vary between individuals; however, expect 1-2 weeks of healing time. In some rare cases the pain is quite severe during the first 48 hours, please contact the clinic with any concerns.
How should the treated area be cared for?
Your doctor or nurse will explain how to care for the treated areas. It is usually advised that, after the dressing has been removed, the area should be washed, bathed or showered as usual. Avoid rubbing the treated area, but gently pat it dry. Within a few days, a scab will form, and the healing process will take several weeks (depending on the part of the body treated). Care must be taken not to scratch the area or accidentally dislodge the scab during the healing process. The use of a suitable sunscreen (SPF 30 or more) following the procedure, especially during outdoor activities, is essential for 48 hours.
Do I need to avoid anything whilst having photodynamic therapy?
Care should be taken not to get the dressing wet when bathing or showering.
It is advisable to avoid swimming until the treated area is fully healed.
What are the potential side effects of photodynamic therapy?
The short-term side effects of phototherapy include:
- Pain (common). When the red light is shone onto the skin, the treated area may hurt. If it is too uncomfortable, your doctor or nurse may suggest pausing treatment for a while, or a local anaesthetic injection may be recommended. After completion of treatment, discomfort and itching may last for a few days, and may require pain-killers.
- Inflammation (common). The treated area may initially become pink, red and puffy, and may crust or ooze a little: this is a normal reaction. It settles within a few days.
- Blistering and ulceration (uncommon). The treated area may occasionally blister or open up (ulcerate) to develop a raw surface.
- Bruising (uncommon). The treated area may occasionally show some bruising.
- Changes in hair growth (uncommon). The treated area may occasionally show increased or loss of hair.
- Dermatitis and contact allergy (uncommon). The treated area may occasionally show signs of dermatitis reaction to the cream or gel applied.
- Infection (uncommon). If the treated area becomes red, swollen and painful, an infection may have developed, and you should contact your doctor.
Potential long-term side effects of phototherapy include:
- Scarring (uncommon). There may be some scarring after PDT.
- Colour change (uncommon). The skin may become darker or paler after PDT.
- Treatment may not be effective, or the condition may come back again. If this happens, you may be offered further PDT, or an alternative type of treatment may be recommended.