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Onychomycosis
is fungal infection of the nail plate, nail bed, or both.
About 10% of the population has onychomycosis. Risk factors include tinea pedis, preexisting nail dystrophy, older age, male sex, and circulatory disease. 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 in the fingers).
Nails have asymptomatic patches of white or yellow discoloration and deformity. There are 3 characteristic presentations: (1) distal subungual, in which the nails thicken and yellow, keratin and debris accumulate distally and underneath, and the nail separates from the nail bed (onycholysis); (2) proximal subungual, a form that starts proximally and is a marker of immunosuppression; and (3) white superficial, in which a chalky white scale slowly spreads beneath the nail surface.
Diagnosis is by appearance and microscopic examination and culture of scrapings. Scrapings are taken from the most proximal position which can be accessed on the affected nail and 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. 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. Differentiation from psoriasis or lichen planus is important, as the therapies differ.
Treatment is oral itraconazole or terbinafine . Itraconazole 200 mg bid 1 wk/mo for 3 mo, or terbinafine 250 mg once/day for 12 wk (6 wk for fingernail), achieves a high cure rate. 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. Topical antifungal nail lacquer containing ciclopirox 8% or amorolfine 5% (not available in US) is rarely effective as primary treatment but can improve cure rate when used as an adjunct with oral drugs, particularly in resistant infections.
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 2005
Content last modified November 2005
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