Onychomycosis

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Description

  • Fungal infection of fingernails/toenails, caused mostly by dermatophytes, less commonly yeasts and nondermatophyte molds
  • Toenails are more commonly affected than fingernails.
  • Synonym: tinea unguium

Epidemiology

Prevalence

  • Worldwide prevalence is approximately 5.5%.
  • More common in adults than children, prevalence increases with age; 35% of adults aged >65 years
  • Rare before puberty
  • Estimated 50% of all nail disorders in the outpatient setting

Etiology and Pathophysiology

  • Inoculation of nail with dermatophytes, non-nondermatophyte molds or yeasts
  • Dermatophytes (60–70%): Trichophyton (Trichophyton rubrum most common), Epidermophyton, Microsporum
  • Yeasts (30–40%): Candida albicans (most common), Candida parapsilosis, Candida tropicalis, Candida krusei
  • Molds: Scopulariopsis brevicaulis, Hendersonula toruloidea, Aspergillus spp., Alternaria tenuis, Cephalosporium, Scytalidium hyalinum
  • Dermatophytes, notably Trichophyton, cause 90% of toenail and 75% of fingernail onychomycoses.
  • Yeasts, especially Candida, may involve fingernails (not uncommonly) or toenails.

Genetics

Possible autosomal dominant inheritance pattern

Risk Factors

  • Older age, occlusive footwear, tinea pedis (particularly interdigital)
  • Cancer, diabetes, psoriasis, peripheral vascular disease
  • Nail injury
  • Living with others with onychomycosis, communal swimming pools
  • Smoking
  • Immunodeficiency

General Prevention

  • Keeping feet cool and dry
  • Avoiding occlusive footwear
  • Using sandals in public locker rooms and swimming pools
  • Discarding or treating infected footwear and socks (1)

Commonly Associated Conditions

  • Immunodeficiency (acquired immune deficiency syndrome and transplant patients), and chronic metabolic disease (e.g., diabetes)
  • Tinea pedis/manuum

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