Photodynamic Therapy (PDT), uses a combination of a photosensitizing medicine and visible light to destroy precancerous cells in actinic keratoses .
The medication, Levulan, contains a substance similar to a by-product of red blood cells called porphyrin. Porphyrins naturally cause an intense destructive reaction in cells that lack an enzyme to break them down when exposed to light. It turns out that precancerous actinic keratoses lack the enzyme to metabolize porphyrins. These cells absorb the medication when it is applied to the skin, but they are simply not able to metabolically clear it like normal cells.
Consequently, when the skin is exposed to visible blue light the abnormal cells are targeted and are eliminated. PDT also is capable of treating invisible (subclinical) damage as well. This results in typically a longer period of clearance of actinic keratoses in the treated area.
The PDT Procedure
The skin is thoroughly cleansed with a degreasing agent like alcohol or acetone and the Levulan is applied directly to the skin. After about one hour of incubation, the treated area is activated with exposure to blue light from a BLU-U light source for about 15 minutes. The combination of Levulan plus the blue light destroys the abnormal actinic keratoses cells. This results in a “sun-burn” type reaction, but it is limited to the abnormal cells.
The photosensitizing effect of the Levulan last 24-48 hours, so it is absolutely critical to stay out of the sun for that period of time. Sun block, hats, scarves and remaining in a dark room are all beneficial to avoid an over reaction. The healing time is very similar to a sun burn, and takes about a week.