Onychomycosis (toe fungus) is notoriously difficult to treat, which can lead to adverse health impacts, particularly in elderly and immunocompromized patients. Current antifungal treatments include systemic and topical drugs. Efficacy of the topical drugs is impaired by their limited ability to penetrate the nail and reach the affected nail bed. Oral systemic antifungals are associated with severe side effects. Light treatments of onychomycosis, therefore, have emerged as an alternative to traditional antifungal therapy due to their minimally invasive nature and the potential for requiring fewer treatment sessions and without systemic side effects.
Due to their minimally invasive nature and potential to restore clear nail growth with relatively few sessions, lasers have become a popular option in the treatment of onychomycosis for both physicians and patients. Laser or light systems that have been investigated for this indication include the carbon dioxide, Nd:YAG, 870/ 930 nm dual wavelength diode laser, and femtosecond infrared 800nm lasers, in addition to photodynamic and ultraviolet light therapy.
The following laser systems are currently FDA approved for a temporary increase in clear nail growth in patients with onychomycosis:
- 1320 nm Nd:YAG
- 1064 nm Nd:YAG
- long-pulsed 1,064-nm
- Nd:YAG Q-switched
- 532 nm output mode Nd:YAG
- 1064 nm Diode
- 980 nm Diode
- 870/930 nm Diode
In one of the earliest studies of lasers treatment onychomycosis, the CO2 was employed. Complete clearance with no recurrence was reported in 75 % of cases after 3 years of follow-up. While results in these reports were promising, the advent of less invasive laser treatment options has made the CO2 laser a less favorable treatment option for onychomycosis.
Nd:YAG laser is the most common laser in medical practice. Its wide availability perhaps was the main reason for use it in studies of lasers treatment onychomycosis. This laser typically emits a 1064nm wavelength, yet 1320nm, and 1440nm wavelengths are also available. In addition, the Nd:YAG laser can operate in continuous, long-pulsed, and high peak power short pulse Q-switched modes. Moreover, the frequency of this laser can be doubled resulting in output wavelength of 532nm.
It is speculated that the 1064 nm Nd:YAG is able to deeply penetrate tissue and efficiently target fungal overgrowth in the nail bed. However, because there are no absorption bands at 1064nm specific to the fungi, it is not clear what would be the mechanism responsible for the fungi destruction. In vitro studies had shown that the Nd:YAG laser significantly inhibits the growth rate of fungi colonies. Clinical studies have also shown some promise. Three studies achieved clinical success using a long-pulse 1064nm Nd:YAG laser. Despite dramatic difference in the fluence during the treatment, ranging between 14 and 223J/cm2, but similar peak power (about 10kW) all reported that several months following treatment, a significant fraction of the patients were clinically clear and culture negative. These studies, however, had a relatively small number of patients, limiting the power of the studies.
Contrary to the long-pulse, recently examined the use of a short pulsed 1064 nm Nd:YAG (PinPointe Footlaser, NuvoLase) laser for onychomycosis in a prospective, randomized, controlled study produced negative results. Use of this particular laser type resulted in neither mycological nor visual improvement.
It was proposed that due to the higher absorption by fat and water, the 1,444-nm Nd:YAG may be better suited for targeting fungal organisms than the 1064nm or 1320nm wavelengths. Unfortunately, only preliminary in-vitro studies had been conducted, which had not to produce conclusive results.
It has also been proposed that the 532nm Nd:YAG may be better at targeting xanthomegnin – the pigment produced by the nail fungus, which has peak absorption between 406 and 555 nm. Akela Laser Corporation has developed high-power laser diode modules operating at 520nm, that represent an inexpensive alternative to the bulky and pricey 532nm Nd:YAG.
Semiconductor diode lasers may represent a better alternative to solid-state lasers in treating onychomycosis, as their wavelength can be selected to target chromophores in the fungus. The 1064nm laser diode can be a direct replacement of much more expensive Nd:YAG. A systematic study in Germany reported positive clinical outcome of laser treatment performed with a 1064-nm diode laser. A protocol similar to the long-pulse Nd:YAG studies were employed, with laser power of 8 W, pulse duration 80 ms, and repetition rate 5.6 Hz. The total energy of 500–800J was applied per session using a spot size of 4 mm and scanning the spot at 2-4mm/s over the entire area of the nail. It is worth noting that the peak power of the semiconductor laser is more than a thousand times lower than that of Nd:YAG. Therefore, the heating of nail appears the major factor in the clinical success. Akela Laser Corporation manufactures best-in-class high-power laser diode modules operating at 1064nm for application in medical devices.
In was discovered in in-vitro studies that high fluences (4,074 J/cm2) of dual wavelength 870/930nm diode laser resulted in 100 % eradication of bacteria, fungi, and yeast. In an attempt to reproduce these positive outcome patients were treated by 870/930nm diode laser with less total energy. While an independent panel noted significant clinical improvement, only about one-third of patients had both clear nail growth and negative mycological cultures. No serious adverse events were reported, and approximately half of the patients complained of the heat and/or tingling. When evaluated at 9-month follow-up, 38 % of patients maintained negative culture and microscopy. Akela Laser Corporation has pioneered multi-wavelengths diode laser modules for the medical application. A wide selection of output power and wavelengths is available.
There are attempts to evaluate the efficacy of the 980-nm diode laser for the treatment of onychomycosis. The 980nm corresponds to te water absorption peak and should be more efficient in heating the tissue than 1064nm. However, there is no published data, yet. Akela Laser Corporation offers high-power laser diode modules operating at 980nm for medical applications.
There was one in-vitro study that investigated the role of UVA (340– 550 nm) light in the treatment of onychomycosis. The authors reported that 40 J/cm2 UVA light was completely fungicidal to T. rubrum on human stratum corneum independent of fungal growth stage. Certain in vitro therapies, however, may not be applicable clinically. Despite being effective in eradicating T. rubrum cultures, UV light, may pose an unnecessary risk when treating live patients. The UV light is a known mutagen and important risk factor in the development of skin cancers.
Photodynamic therapy Photodynamic therapy (PDT) is the most studied light therapy for onychomycosis which is the combination of a photosensitizing agent followed by irradiation with a specific wavelength of light, thus enabling maximal absorption of light by the desired target. When using PDT for onychomycosis, the causative organism absorbs the photosensitizing agent, making it more susceptible to destruction than surrounding healthy tissue. While many photosensitizers have been evaluated for this purpose, 5-aminolevulinic acid (5-ALA) is the most frequently studied due to conversion of 5-ALA to protoporphyrin IX by fungi. Protophorphyrin IX possesses peak wavelength absorption between 630 and 700 nm, making it easily targeted by the red light. Akela Laser Corporation offers a wide selection of laser modules in this wavelength range, as well as a turn-key system for medical applications.