Lasers promising for onychomycosis treatment
EXPERT ANALYSIS FROM CONTROVERSIES AND CONVERSATIONS IN LASER AND COSMETIC SURGERY
DANA POINT, CALIF. – Lasers are playing a key role in the treatment of onychomycosis, with cure rates exceeding that of terbinafine in most cases, Dr. Jill S. Waibel said at a meeting sponsored by SkinCare Physicians and Northwestern University.
The development is welcome because currently approved treatment options are "suboptimal," said Dr. Waibel, a dermatologic surgeon with Miami (Fla.) Dermatology & Laser Institute. "There’s also a big need; 34% of diabetics have onychomycosis. They are at an increased risk of developing complications including foot ulcers and amputations. In addition, 50% of individuals over age 70 have onychomycosis. The market for treatment in the United States is $1.6 billion," she said.
All infectious agents can be killed by heat except prions, which makes laser therapy a promising option for onychomycosis, Dr. Waibel said. The mechanism of action is not fully understood, but she shared three hypotheses. The first is that water in the keratin of the nail absorbs the laser energy and creates nonspecific bulk heating, which denatures fungal organelles. The second hypothesis is that free radicals are created by the laser, and these kill the dermatophyte. The third hypothesis is that microscopic selective photothermolysis occurs in Trichophyton species that contain melanin in their cell walls. Microcavitation and acoustic shock waves are created, which decapsulate the spores. The mechanism of action "is probably a combination of all three," she speculated.
Before laser treatment, the patient’s toenails and the surrounding skin are cleaned, and photos are taken of the nails, Dr. Waibel said. The affected areas of nail are treated with randomly assigned laser or light wavelengths until a temperature of 46° C is reached.
"The thicker the nail, the more energy we put into it," Dr. Waibel said of the treatment. "For every 5° C increase in temperature, there is an exponential decrease in the time to cell death. When laser energy first strikes the nail bed, there is a rapid spike in temperature reaching the lower 60° C range," she explained. "If you’re at 60° C, it only takes about 6 seconds to kill the dermatophyte. At 70° C, that takes about 6 ms, so the lasers are getting to the temperature to kill the dermatophyte."