Laser Therapy for Onychomycosis: Fact or Fiction?

Keywords:laser therapy, surgical fiber,  Time:18-03-2016

Onychomycosis is a common fungal infection, afflicting some 10% of the adult population in industrialized countries. Aside from cosmetic concerns, onychomycosis can be the cause of toe and foot pain, as well as the underlying etiology for serious secondary bacterial infections and traumatic ulcerations. In select populations, such as diabetics,  the latter conditions may even result in loss of all or part of the lower extremity. Thus,  a simple, cost-effective and safe treatment for onychomycosis is highly desirable. Although both topical and oral systemic antifungal agents are available for this purpose, they are not always effective, carry some medical risks, are associated with potentially significant  drug-drug interactions, and may be unacceptable to patient and healthcare provider alike. Physical modalities, such as laser therapy, therefore appear appealing. The question is whether laser treatment is sufficiently efficacious and safe to warrant the current high cost per treatment. The readily available literature on this controversy will be reviewed herein.

Onychomycosis is a fungal infection of the nail that poses a significant treatment challenge, as it is often completely or partially refractory to approved topical and systemic medications. Estimated to  affect 2%–10% of the population, onychomycosis is the most common pathology of the nail, comprising 18%–40% of all nail disorders [1,2]. The predominant nail pathogens are dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes, though yeasts and non-dermatophyte molds may also be etiologic, particularly in diabetic and immunosuppressed patients. Fungi colonize the nail plate, bed, and matrix, leading to discoloration of the nail, thickening of the subungual region, and, when advanced, onycholysis [3,4]. Beyond cosmetic concern, onychomycosis may lead to secondary bacterial infections and predispose to erysipelas and cellulitis [5]. In the diabetic population, jagged onychomycotic toenails may injure the adjacent tissue and thus increase the risk of foot ulcer, with sepsis or amputation a potential consequence [6].

Systemic antifungal drugs are the mainstay of therapy for this chronic disease. When taken for a  12-week course, oral terbinafine has a mycologic cure rate of 71%–82% and a maximal clinical response rate of 60%–70% [7,8]. However, patients are often poorly compliant with the lengthy duration of treatment, resulting in sub-therapeutic concentrations reaching the nail plate [9]. Additionally, terbinafine can elevate liver enzymes and has rarely progressed to fulminant liver failure. Accordingly, it requires routine blood testing and is contraindicated in patients with chronic or active liver disease [10]. Additional adverse events include headache, loss of taste, and abdominal discomfort and induction of  a lupus-like syndrome. Itraconazole, another FDA-approved systemic antifungal drug utilized to manage onychomycosis, has much lower mycologic and clinical clearing rates, and may induce cardiac toxicity; it is also associated with a plethora of drug-drug interactions, making it an equally unattractive  treatment modality.

In light of these limitations, laser therapy has been proposed as an alternative option for onychomycosis therapy. Currently utilized for a wide variety of medical and cosmetic skin disorders, dermatological lasers, supporters argue, offer a convenient solution with minimal side effects [11]. Treatment is administered in the medical setting (office/hospital), thus eliminating the requirement for patient adherence. Laser therapy also has the potential to treat those patients where systemic antifungals are either contraindicated or associated with possible drug-drug interactions [4]. Although the mechanism of action remains unknown, several theories exist. By the principle of selective photothermolysis, based on differences in thermal conductivity, laser energy may be preferentially absorbed by fungal pathogens resulting in photothermal and photomechanical damage  that spares surrounding human tissues [4,12]. An alternate theory suggests the formation of free radicals by incident laser energy and light absorption by fungal pigment xanthomegnin, present in high concentration in Trichophyton rubrum [13].