NEW ORLEANS - Lasers and photodynamic therapy for the treatment of fungal toenails are beginning to generate substantial buzz among patients and podiatrists, but key questions regarding these novel proposed device therapies remain to be answered before they can truly be said to be the future of onychomycosis therapy.
For laser therapy, these questions include "Does it actually work?" and if so, by what mechanism? Dr. Boni E. Elewski said at the annual meeting of the American Academy of Dermatology.
Dr. Boni E. Elewski
Interest in laser therapy for fungal nails took off when one device, the PinPointe FootLaser, received Food and Drug Administration clearance for onychomycosis last October. Of note, however, the FDA didn't clear the device as a curative therapy, but rather "for the temporary increase of clear nail in patients with onychomycosis." This hasn't stopped some podiatrists from offering treatment with the PinPointe or other neodymium:YAG 1,064-nm lasers at a price tag of up to $1,000 per toe, a marketing ploy that implies definitive therapy and prompted Dr. Elewski to take a closer look.
Her in vitro studies in the mycology lab have left her convinced that lasers don't eradicate fungi through heat killing; the required nail temperatures would be intolerably painful. Moreover, direct lasering of fungi on agar plates and dilute broth had absolutely no impact on fungal growth. But these negative studies don't rule out other potential mechanisms of action, including a possible immunologic effect or laser-induced denaturization of enzymes that fungi need to digest skin cells, noted Dr. Elewski, professor of dermatology at the University of Alabama at Birmingham.
She is now conducting a clinical study in which patients with onychomycosis are being treated with an Nd:YAG 1,064-nm laser – not the PinPointe FootLaser – with a 5-mm spot size, a frequency of 2 Hz, and an energy density of 16 J/cm2. Patients get a total of five treatments, each consisting of more than 300 pulses administered over the nail during a couple of minutes in a predetermined pattern. Anecdotally, in individual patients she has observed instances of fungi evacuating laser-treated nails, and the nails becoming culture negative over a period of several months. The study, however, remains ongoing.
"The jury is still out. I can't say yet whether laser therapy works," Dr. Elewski commented.
Unlike laser therapy for onychomycosis, photodynamic therapy (PDT) is backed by a published rigorously conducted study. And the mechanism of action is understood: In vitro, Trichophyton rubrum absorbs 5-aminolevulinic acid and can be photo killed.
But onychomycosis is not an FDA-approved indication for PDT. Moreover, the results of the published study cited by Dr. Elewski – a 43% cure rate 12 months after PDT and 37% at 18 months of follow-up – are comparable to but not better than success rates attained in the major clinical trials of terbinafine. Plus, the PDT sessions must be preceded by a lengthy, labor-intensive chemical nail avulsion. Nonetheless, PDT may provide an alternative option for onychomycosis when terbinafine and other oral agents are contraindicated, she continued.
The PDT study involved 30 patients with onychomycosis resulting from Trichophyton rubrum who were treated at Aristotle University of Thessaloniki (Greece). Following 10 consecutive nights in which 20% urea ointment was applied under occlusion to the nail plate, dermatologists removed the nail with forceps and applied 20% 5-aminolevulinic acid for 3 hours before treatment with red light at 570-670 nm, a light density of 40 J/cm2, and a fluence of 40 mW/cm2. Patients got three treatment sessions, each 2 weeks apart.
The Greek investigators demanded a rigorous, FDA-style definition of cure: complete absence of clinical signs of fungal infection, or less than 10% of the nail being affected by subungual hyperkeratosis along with mycologic cure. Thirteen of 30 (43%) patients fulfilled this definition at 12 months, as did 11 (37%) at 18 months. No fungal resistance was seen (Acta Derm. Venereol. 2010;90:216-7).
Dr. Elewski said that she receives research support from Cutera.