What is the mechanism of action for laser treatment for onychomycosis of the toenails?—Elizabeth McDonough, PA-C, Naples, Fla.

Onychomycosis is a nail infection caused by a fungus, yeast, or mold. Toenail onychomycosis is most commonly caused by dermatophytes, or fungus. Risk factors include age, diabetes, immunodeficient status, swimming, tinea pedis, psoriasis, and living with others who have onychomycosis.

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The paucity of data on the efficacy and the mechanisms of action of laser therapy for onychomycosis makes it difficult to answer this question. According to the literature, proposed mechanisms of action for laser therapy for onychomycosis include direct fungicidal effects, inhibition of fungus by laser-induced changes in the tissue environment, and laser-induced immunologic effects, though an in vitro study evaluating the effects of a submillisecond Nd:YAG laser on fungal nail pathogens did not find support for a laser-induced direct fungicidal effect.

Further study with randomized trials that compare laser devices with placebo and other onychomycosis treatments, as well as long-term follow-up studies, will be useful for clarifying the efficacy, mechanisms, optimal regimens, and indications for laser therapies.—LAURA FOSTER, CRNP, FNP, practices family medicine with Palmetto Primary Care Physicians in Charleston, S.C. (207-4)

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