Photodynamic Therapy
Photodynamic therapy (PDT) combines a prescription light-sensitive cream, usually Metvix (methyl aminolevulinate), with a suitable light source. The cream is applied to the lesion and a small margin of surrounding skin. Light activation produces a reaction that damages targeted abnormal cells. The effect is relatively selective, but the treated area and immediately surrounding skin can still become red, swollen, sore or crusted.
Metvix PDT may be considered for thin, non-pigmented actinic keratoses and selected superficial or nodular basal cell carcinomas when other treatments are unsuitable. It may also be used for selected cases of Bowen's disease following specialist assessment. Suitability depends on the diagnosis, thickness, depth, pigmentation, site and previous treatment.
PDT is not appropriate for every lesion. Thick, deeply infiltrating or pigmented lesions may need a different approach. Clearance and recurrence rates vary, so your dermatologist will discuss the alternatives and arrange the follow-up appropriate to your diagnosis.
What does the procedure involve?
A conventional red-light PDT appointment has two stages on the same day. First, the surface of the lesion is prepared by removing scale or crust. Metvix cream is then applied to the lesion and a small margin of surrounding skin and covered with a dressing for three hours.
The dressing and cream are removed, and the area is immediately exposed to a suitable red light. The illumination time depends on the equipment and prescribed light dose.
The number of sessions depends on the diagnosis. Actinic keratoses are generally treated in one session and reviewed after about three months, with retreatment if required. Selected basal cell carcinomas are generally treated in two sessions one week apart and reviewed after about three months. Your dermatologist will confirm the plan for your lesion.
Benefits and alternatives
PDT can avoid excision in selected cases and may offer a useful cosmetic outcome, but it is not the best option for every lesion and recurrence can occur. Alternatives may include prescription creams, cryotherapy, curettage or surgical excision. Your dermatologist will explain the expected benefits, limitations and alternatives for your diagnosis.
What are the possible side effects?
Burning, stinging or pain can occur during illumination and can occasionally be intense. Cooling and other pain-relief measures may be used. Afterwards, redness, swelling, tenderness, itching, crusting or weeping can occur and may last one to two weeks, occasionally longer.
Other local reactions can include blistering, ulceration, peeling, bleeding, infection and temporary lighter or darker pigmentation. Scarring has also been reported. Allergic reactions are uncommon but possible.
Protect the treated area and surrounding skin from sunlight for a couple of days and follow the individual aftercare instructions provided by your treatment team. Seek urgent medical help for swelling of the face, tongue or throat or difficulty breathing. Contact the clinic if pain is severe, the area appears infected or healing is not progressing as expected.