The effectiveness of lasers in the treatment of onychomycosis: a systematic review Part 1 of 3.
Lasers have been a part of podiatric practice for many years. Papers discussing their potential uses in clinical practice started to appear in the 1980s, particularly focussing on the high powered carbon dioxide (CO2) systems available at that time [1-3]. Much of this work discussed their ablative abilities in nail matrixectomies and their early potential for onychomycosis following total nail ablation  and by nail fenestration to improve topical drug delivery  but generally their use remained in the hands of a few specialist practitioners, mainly in the USA. This continued for several years with newer systems being slowly introduced such as the pulsed dye laser, which has been explored as a treatment for plantar warts with varying levels of success [5-8]. The expense of these early systems was prohibitive for everyday practice and so their use was limited.
In 2009, for the first time a surgical laser system was advertised in the UK Podiatry magazine Podiatry Now indicated for the treatment of onychomycosis. Shortly afterwards, a letter was published suggesting that this was "possibly the most radical development in the treatment of onychomycosis our profession has ever seen". Some concerns were expressed at the unproven efficacy of these new devices and the investment costs involved . In addition, despite it now being nearly five years since their first introduction into practice little evidence has appeared in the professional literature demonstrating their effectiveness despite their introduction into UK clinics, evident through internet searches, offering this treatment modality. Similar concerns have been expressed in the dermatological fields with laser systems for onychomycosis being "praised uncritically and promoted at high prices" .
Lasers systems are attractive for the practitioner and public alike for a number of reasons. Oral drug regimens have showed effectiveness in many studies and remain the most studied intervention for this condition.
However, debate is always raised about the safety of oral drugs, despite many years' experience with these agents and safety reporting [12,13]. Antifungal drugs, like many others, are contra-indicated in patients with active or chronic liver disease and are sometimes declined by patients seeking alternatives to oral medication--often to avoid potential for side-effects. Topical agents too, are considered by many to be a protracted and frequently ineffective intervention as patient compliance over the treatment period can be an issue. Lasers are often marketed as a means of improving a practice's income and are seen as an investment which can pay for itself in a short period of time. Lasers also capture the imagination of the public as a safe, effective quick fix for a range of clinical conditions.
The proposed mechanism of action of lasers in the treatment of onychomycosis remains unclear. However, laser systems in near infrared spectrum (780nm-3000nm wavelength), which are commonly used in onychomycosis, exert their effect by direct heating of the target tissues . Moreover, by using a pulsed beam instead of continuous beam, these lasers can deliver a "selective photothermolysis" delivering of a short burst of laser light energy into the target tissue causing a rapid elevation in temperature into the defined target area. Sufficient intervals between pulses can allow for tissue relaxation and cooling to occur, causing very little collateral damage to surrounding structures. In the laboratory, eradication of the common dermatophyte Trichophyton rubrum has been demonstrated using pulsed laser technology . Studies on fungal nail clippings have demonstrated this to have a direct thermal killing effect on fungal mycelia when treatment temperatures exceed 50[degrees] centigrade .
Lasers for nail disease have been approved in the United States by the Food and Drug Administration (FDA). To date, devices have been approved only on their ability to temporary clear nail growth in onychomycotic nails, and not on definitive curative data. Consequently evaluation of their capabilities remains a necessity to inform practitioners of their effectiveness in the longer term. A literature review published in 2013 which, in part, discussed laser technology in onychomycosis concluded that evidence was lacking due to small scale studies and poor design however, this was not systematic. Consequently, the author has undertaken a systematic literature review to assess the published results and evidence of effectiveness to date.
This study was compiled adopting the "Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines" . Any original study, published in a peer reviewed journal, which examined the use of a laser technology in the treatment of onychomycosis (in more than a single case) was considered for inclusion. The primary outcome measure was efficacy, only including studies which employed microbiological or histological procedures to establish an initial diagnosis of the condition, and subsequently measured the outcome either by a repeated microbiological/histological assessment or measured changes in physical nail clearance of discolouration following treatment. Studies which did not follow this procedure were excluded, as were those which stated they exclusively studied fingernail onychomycosis.
An electronic database search was undertaken using PubMed (US National Library of Health Database [June 2014]) and Web of Science[R] (June 2014) to identify papers which met the initial inclusion criteria. Searches were standardized using a combination of the keywords "ony-chomycosis", "tinea unguium", "laser", "nail", "rubrum". No date limits were set, but as a relatively new modality, papers over six years old were unlikely. The initial search yielded a total of 268 potential papers. All abstracts were reviewed to remove duplicates and to remove papers which did not meet the inclusion criteria. Papers which met the inclusion parameters were then read in hull by the author. Only papers written in English, with full study details available were included in the final suite of papers. This exercise was repeated twice by the author to improve the reliability of the search end prevent eligible papers being missed or excluded (Figure 1).
Following the selection process, remaining papers were evaluated for their level of evidence using two systems as adopted by Matricciani et al.. Firstly, papers were graded using the National Health and Medical Research Council (NHMRC) Hierarchy of Evidence  scale (see Additional file 1) and subsequently the American Occupational Therapy Association (AOTA) Evidence based literature Review Project, as adapted by Trombly and Ma  (see Additional file 2) as a means to identify threats to validity within the included studies. This system allowed for the objective assessment of published research, graded on the four dimensions of design sample size, internal validity and external validity.
The Results from this study will be published in the next issue of Podiatry Review
References and End Notes (for part 1)
AOTA: American Occupational Therapy Association; DLSO: Distal lateral subungual onychomycosis; FDA: Food and Drug Administration; Nd: YAG: Neodymium:Yttrium Aluminum Garnet (laser); OSI: Onychomycosis severity index; PAS: Periodic Acid-Schiff stain; PCR: Polymerase Chain Reaction; PWSO: Proximal white sub-ungual onychomycosis; RCT: Randomised Controlled Trial; SWO: Superficial white onychomycosis; TDO: Total dystrophic onychomycosis.
The author declares he has no competing interests.
IB was responsible for the drafting of the paper and conducting the review. All authors read and approved the final manuscript.
Received: 15 April 2014 Accepted: 17 July 2014
Published: 27 July 2014
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Written by Ivan Bristow
Bristow: The effectiveness of lasers in the treatment of onychomycosis: a systematic review. Journal of Foot and Ankle Research 2014 7:34.Submit
Caption: Figure 1 Flow Diagram of search strategy (conducted June 2014).
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