PDT May Surpass Laser for Port Wine Stain Clearance

MONT TREMBLANT, QUE. — Photodynamic therapy for port wine stains could improve the low success rates of traditional pulsed dye laser therapy, because it overcomes the barrier of thermal confinement, according to J. Stuart Nelson, M.D., who spoke at a symposium on cutaneous laser surgery sponsored by SkinCare Physicians of Chestnut Hill.

"The problem we have with current treatment is that port wine stains are made up of blood vessels of very different sizes—but based on the pulse duration and the wavelength of the laser treatment you choose, you only get thermal confinement of certain blood vessels," said Dr. Nelson of the Beckman Laser Institute at the University of California, Irvine.

"If you inject photosensitizers intravenously into the port wine stain's blood vessels and then you irradiate with the wavelength that is absorbed by the photosensitizer, you get destruction of the endothelial cells, wherever the photosensitizer is," he said in an interview.

His group has internal review board approval to use this approach under an experimental protocol that excludes children, facial lesions, and lesions larger than 2 cm.

"It boils down to us working out the appropriate drug and light dissymmetry parameters for human skin. We are currently using a benzoporphyrin derivative called verteporfin with great success. This is a drug used for macular degeneration, which is confined to the vascular compartment, where we want it, and has also had extensive clinical use—so there are no issues there," he said.

But Dr. Nelson stressed that the key to safety with this approach is real-time in situ vascular monitoring using a technique called optical Doppler flow tomography.

"What happens in PDT is that you get a slowing down of the blood flow as the endothelial cells are injured. And so what we wanted to be able to do is to monitor that change in blood flow. You can't just arbitrarily irradiate; otherwise, you are going to get into problems. The good thing about PDT is that is destroys all the blood vessels, but that is the dangerous thing about it too," he said.