Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails typically are deformed and discolored white or yellow. Diagnosis is by appearance, wet mount, culture, PCR, or a combination. Treatment, when indicated, is with oral terbinafine or itraconazole.
About 10% (range 2 to 14%) of the population has onychomycosis. Risk factors include
Toenails are 10 times more commonly infected than fingernails. About 60 to 80% of cases are caused by dermatophytes (eg, Trichophyton rubrum); dermatophyte infection of the nails is called tinea unguium. Many of the remaining cases are caused by nondermatophyte molds (eg, Aspergillus,Scopulariopsis,Fusarium). Immunocompromised patients and those with chronic mucocutaneous candidiasis may have candidal onychomycosis (which is more common on the fingers). Subclinical onychomycosis can also occur in patients with recurrent tinea pedis. Onychomycosis may predispose patients to lower extremity cellulitis.
Symptoms and Signs
Nails have asymptomatic patches of white or yellow discoloration and deformity. There are 3 common characteristic patterns:
Onychomycosis is suspected by appearance; predictive clinical features include involvement of the 3rd or 5th toenail, involvement of the 1st and 5th toenails on the same foot, and unilateral nail deformity. Subclinical onychomycosis should be considered in patients with recurrent tinea pedis. Differentiation from psoriasis or lichen planus is important because the therapies differ, so diagnosis is typically confirmed by microscopic examination and, unless microscopic findings are conclusive, culture of scrapings or rarely PCR of clippings. Scrapings are taken from the most proximal position that can be accessed on the affected nail and are examined for hyphae on potassium hydroxide wet mount and cultured. Obtaining an adequate sample of nail can be difficult because the distal subungual debris, which is easy to sample, often does not contain living fungus. Therefore, removing the distal portion of the nail with clippers before sampling or using a small curette to reach more proximally beneath the nail increases the yield. PCR can be done if cultures are negative and the cost of finding a definitive diagnosis is warranted.
Onychomycosis is not always treated because many cases are asymptomatic or mild and unlikely to cause complications, and the oral drugs that are the most effective treatments can potentially cause hepatotoxicity and serious drug interactions. Some proposed indications for treatment include the following:
Treatment is oral terbinafine or itraconazole. Terbinafine 250 mg once/day for 12 wk (6 wk for fingernail) achieves a cure rate of 75 to 80% and itraconazole 200 mg bid 1 wk/mo for 3 mo achieves a cure rate of 40 to 50%, but the recurrence rate is estimated to be as high as 10 to 50%. It is not necessary to treat until all abnormal nail is gone because these drugs remain bound to the nail plate and continue to be effective after oral administration has ceased. The affected nail will not revert to normal; however, newly growing nail will appear normal.
Investigative treatments that have less frequent and/or less severe adverse effects and show promise include laser therapy, new formulations of topical agents (including efinaconazole), and new delivery systems for terbinafine. Topical antifungal nail lacquer containing ciclopirox 8% or amorolfine 5% (not available in the US) is occasionally effective as primary treatment (cure rate of about 30%) and can improve cure rate when used as an adjunct with oral drugs, particularly in resistant infections. A topical formulation containing eucalyptus oil, camphor, menthol, thymol, oil of turpentine, oil of nutmeg, and oil of cedar leaf (as in the OTC chest rub preparation Vicks®VapoRub®) has antifungal properties and has been effective in some patients.
To limit relapse, the patient should trim nails short, dry feet after bathing, wear absorbent socks, and use antifungal foot powder. Old shoes may harbor a high density of spores and, if possible, should not be worn.
Last full review/revision November 2013 by Wingfield E. Rehmus, MD, MPH
Content last modified November 2013