|Classification and external resources|
A toenail affected by onychomycosis
Onychomycosis (also known as "dermatophytic onychomycosis," "ringworm of the nail," and "tinea unguium") means fungal infection of the nail. It is the most common disease of the nails and constitutes about a half of all nail abnormalities.
There are four classic types of onychomycosis:
- Distal subungual onychomycosis is the most common form of tinea unguium, and is usually caused by Trichophyton rubrum, which invades the nail bed and the underside of the nail plate.
- White superficial onychomycosis (WSO) is caused by fungal invasion of the superficial layers of the nail plate to form "white islands" on the plate. It accounts for only 10 percent of onychomycosis cases. In some cases, WSO is a misdiagnosis of "keratin granulations" which are not a fungus, but a reaction to nail polish that can cause the nails to have a chalky white appearance. A laboratory test should be performed to confirm.
- Proximal subungual onychomycosis is fungal penetration of the newly formed nail plate through the proximal nail fold. It is the least common form of tinea unguium in healthy people, but is found more commonly when the patient is immunocompromised.
- Candidal onychomycosis is Candida species invasion of the fingernails, usually occurring in persons who frequently immerse their hands in water. This normally requires the prior damage of the nail by infection or trauma.
Signs and symptoms 
The most common symptom of a fungal nail infection is the nail becoming thickened and discoloured: white, black, yellow or green. As the infection progresses the nail can become brittle, with pieces breaking off or coming away from the toe or finger completely. If left untreated, the skin can become inflamed and painful underneath and around the nail. There may also be white or yellow patches on the nailbed or scaly skin next to the nail. There is usually no pain or other bodily symptoms, unless the disease is severe. People with onychomycosis may experience significant psychosocial problems due to the appearance of the nail, particularly when fingers – which are always visible – rather than toenails are affected.
Dermatophytids are fungus-free skin lesions that sometimes form as a result of a fungus infection in another part of the body. This could take the form of a rash or itch in an area of the body that is not infected with the fungus. Dermatophytids can be thought of as an allergic reaction to the fungus.
The causative pathogens of onychomycosis include dermatophytes, Candida, and nondermatophytic molds. Dermatophytes are the fungi most commonly responsible for onychomycosis in the temperate western countries; while Candida and nondermatophytic molds are more frequently involved in the tropics and subtropics with a hot and humid climate.
Trichophyton rubrum is the most common dermatophyte involved in onychomycosis. Other dermatophytes that may be involved are T. interdigitale, Epidermophyton floccosum, T. violaceum, Microsporum gypseum, T. tonsurans, T. soudanense (considered by some to be an African variant of T. rubrum rather than a full-fledged separate species) and the cattle ringworm fungus T. verrucosum. A common outdated name that may still be reported by medical laboratories is Trichophyton mentagrophytes for T. interdigitale. The name T. mentagrophytes is now restricted to the agent of favus skin infection of the mouse; though this fungus may be transmitted from mice and their danders to humans, it generally infects skin and not nails.
Other causative pathogens include Candida and nondermatophytic molds, in particular members of the mold generation Scytalidium (name recently changed to Neoscytalidium), Scopulariopsis, and Aspergillus. Candida spp. mainly cause fingernail onychomycosis in people whose hands are often submerged in water. Scytalidium mainly affects people in the tropics, though it persists if they later move to areas of temperate climate.
Other molds more commonly affect people older than 60 years, and their presence in the nail reflects a slight weakening in the nail's ability to defend itself against fungal invasion.
Risk factors 
Aging is the most common risk factor for onychomycosis due to diminished blood circulation, longer exposure to fungi, and nails which grow more slowly and thicken, increasing susceptibility to infection. Nail fungus tends to affect men more often than women, and is associated with a family history of this infection
Other risk factors include perspiring heavily, being in a humid or moist environment, psoriasis, wearing socks and shoes that hinder ventilation and do not absorb perspiration, going barefoot in damp public places such as swimming pools, gyms and shower rooms, having athlete's foot (tinea pedis), minor skin or nail injury, damaged nail, or other infection, and having diabetes, circulation problems, which may also lead to lower peripheral temperatures on hands and feet, or a weakened immune system.
To avoid misdiagnosis as nail psoriasis, lichen planus, contact dermatitis, trauma, nail bed tumor or yellow nail syndrome, laboratory confirmation may be necessary. The three main approaches are potassium hydroxide smear, culture and histology. This involves microscopic examination and culture of nail scrapings or clippings. Recent results indicate the most sensitive diagnostic approaches are direct smear combined with histological examination, and nail plate biopsy using periodic acid-Schiff stain. To reliably identify nondermatophyte molds, several samples may be necessary.
Treatment of onychomycosis is challenging because the infection is embedded within the nail and is difficult to reach; full removal of symptoms is slow and may take a year or more, since new nail growth must entirely replace old, infected growth.
Most treatments are either systemic antifungal medications, such as clotrimazole, terbinafine and itraconazole, or topical, such as nail paints containing ciclopirox (ciclopiroxolamine) or amorolfine. There is evidence that combining systemic and topical treatments is beneficial.
For superficial white onychomycosis, systemic rather than topical antifungal therapy is advised.
In July 2007 a meta-study reported on clinical trials for topical treatments of fungal nail infections. The study included six randomised, controlled trials dating up to March 2005. The main findings are:
- There is some evidence ciclopiroxolamine and butenafine are both effective, but both need to be applied daily for prolonged periods (at least 1 year).
- There is evidence topical ciclopiroxolamine has poor cure rates, and that amorolfine might be substantially more effective.
- Further research into the effectiveness of antifungal agents for nail infections is required.
A 2002 study compared the efficacy and safety of medication with terbinafine in comparison to placebo, itraconazole and griseofulvin in treating fungal infections of the nails. The main findings were for reduced fungus, terbinafine was found to be significantly better than itraconazole and griseofulvin, and terbinafine was better tolerated than itraconazole.
- A small study in 2004 showed ciclopirox nail paint was more effective when combined with topical urea cream.
- A study of 504 patients in 2007 found aggressive debridement of the nail, combined with oral terbinafine, significantly reduced symptom frequency over terbinafine alone.
- A 2007 randomised clinical trial with 249 patients showed a combination of amorolfine nail lacquer and oral terbinafine enhanced clinical efficacy and is more cost-effective than terbinafine alone.
Research suggests that fungi are sensitive to heat, typically 40–60 °C. The basis of laser treatment is to try heat the nail bed to these temperatures in order to disrupt fungal growth.
A Noveon-type laser, already in use by physicians for some types of cataract surgery on the eye, is used by some podiatrists, although the only scientific study on its efficacy as of 2010[update], while showing positive results, included far too few test subjects for the laser to be proven generally effective.
Several companies have approval to market a Nd:YAG laser for onychomycosis treatment.
The wavelength of light produced by the lasers trialled is in the visible or infra-red range, and insufficiently high to produce direct dna damage as would be the case with ultra-violet lasers.
If heating is an effective treatment, then there would be many other low technology, low cost methods available to raise the temperature of the nail bed, including infra-red heating, warm air heating etc.
- Vicks VapoRub has been used as an effective onychomycosis treatment.
- Australian tea tree oil has been tested, but there is insufficient information to make recommendations for its use for onychomycosis.
- Grapefruit seed extract as a natural antimicrobial is not demonstrated. Its effectiveness is scientifically unverified. Multiple studies indicate the universal antimicrobial activity is due to contamination with synthetic preservatives that were unlikely to be made from the seeds of the grapefruit.
- Snakeroot (Ageratina pichinchensis) leaf extract has, in studies, shown ability to treat superficial onychomycosis. The results show its effectiveness is less than ciclopirox, and equal to ketaconazole.
- Thymol, the active ingredient in thyme oil, has been shown to be effective against the fungi that cause Onychomycosis.
Nail fungus can be painful and cause permanent damage to nails. It may lead to other serious infections if the immune system is suppressed due to medication, diabetes or other conditions. The risk is most serious for people with diabetes and with immune systems weakened by leukaemia or AIDS, or medication after organ transplant. Diabetics have vascular and nerve impairment, and are at risk of cellulitis, a potentially serious bacterial infection; any relatively minor injury to feet, including a nail fungal infection, can lead to more serious complications. Osteomyelitis (infection of the bone) is another, rare, possible complication.
A 2003 survey of diseases of the foot in 16 European countries found onychomycosis to be the most frequent fungal foot infection and estimates its prevalence at 27%. Prevalence was observed to increase with age. In Canada, the prevalence was estimated to be 6.48%. Onychomycosis affects approximately one-third of diabetics and is 56% more frequent in people suffering from psoriasis.
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