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A 29-year-old woman presents with thickened and discolored toenails for 1 year (Figure 193-1). She is embarrassed to wear sandals and wants treatment. The entire nail plates are involved and there is subungual keratosis. She did not realize that she had tinea pedis, but a fine scale was seen on the soles and sides of the feet indicative of tinea pedis in a moccasin distribution. A KOH scraping from the subungual debris was positive for hyphae. She has no history of liver disease or risk factors for liver disease. An oral antifungal was prescribed for 3 months.

Figure 193-1

Onychomycosis in all toenails of this 29-year-old woman. Note the nail plate thickening and discoloration along with the subungual keratosis. She also has tinea pedis in a moccasin distribution. (Courtesy of Richard P. Usatine, MD.)

Onychomycosis is a term used to denote nail infections caused by any fungus, including dermatophytes, yeasts, and nondermatophyte molds. One, some, and occasionally all of the toenails and/or fingernails may be involved. Although most toenail onychomycosis is caused by dermatophytes, many cases of fingernail onychomycosis are caused by yeast. Onychomycosis may involve the nail plate and other parts of the nail unit, including the nail matrix.

Toenail fungus, tinea unguium, dermatophytosis of nails.

  • The incidence of onychomycosis has been reported to be 2% to 13% in North America.1
  • Most patients (7.6%) only have toenail involvement and only 0.15% have fingernail involvement alone.2
  • The prevalence of onychomycosis varies from 4% to 18%.3,4
  • The disease is very common in adults, but may also occur in children.

  • Dermatophytes are responsible for most finger and toenail infections.
  • Nonpathogenic fungi and Candida (in the rare syndrome of chronic mucocutaneous candidiasis) also can infect the nail plate (Figure 193-2).
  • Dermatophytic onychomycosis (tinea unguium) occurs in three distinct forms: distal subungual, proximal subungual, and white superficial.
  • The vast majority of distal and proximal subungual onychomycosis results from Trichophyton rubrum (Figure 193-3).
  • White superficial onychomycosis is usually caused by Trichophyton mentagrophytes, although cases caused by T. rubrum have also been reported (Figure 193-4).
  • Yeast onychomycosis is most common in the fingers caused by Candida albicans.

Figure 193-2

Candida infection of the skin and nails in an immunosuppressed patient with chronic mucocutaneous candidiasis. (Courtesy of Richard P. Usatine, MD.)

Figure 193-3

Severe toenail onychomycosis demonstrating subungual keratosis in the first nail and onychogryphosis (ram's horn nail) in the second nail because of the fungal infection. The culture grew Trichophyton rubrum. (Courtesy of Richard P. Usatine, MD.)

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