Onychomycosis 

  • Author: Antonella Tosti, MD; Chief Editor: Dirk M Elston, MD   more...
 
Updated: May 5, 2010
 

Background

Onychomycosis (OM) refers to a fungal infection that affects the toenails or the fingernails. Onychomycosis may involve any component of the nail unit, including the nail matrix, nail bed, or nail plate. Onychomycosis is not life threatening, but it can cause pain, discomfort, and disfigurement and may produce serious physical and occupational limitations. Psychosocial and emotional effects resulting from onychomycosis are widespread and may have a significant impact on quality of life.[1]

The main subtypes of onychomycosis are distal lateral subungual onychomycosis (DLSO), white superficial onychomycosis (WSO), proximal subungual onychomycosis (PSO), endonyx onychomycosis (EO), and candidal onychomycosis. Patients may have a combination of these subtypes. Total dystrophic onychomycosis refers to the most advanced form of any subtype.

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Pathophysiology

The pathogenesis of onychomycosis depends on the clinical subtype. In distal lateral subungual onychomycosis, the most common form of onychomycosis, the fungus spreads from plantar skin and invades the nail bed via the hyponychium. Inflammation occurring in these areas of the nail apparatus causes the typical physical signs of distal lateral subungual onychomycosis. In contrast, white superficial onychomycosis is a rarer presentation caused by direct invasion of the surface of the nail plate. In proximal subungual onychomycosis, the least common subtype, fungi penetrate the nail matrix via the proximal nail fold and colonize the deep portion of proximal nail plate. Endonyx onychomycosis is a variant of distal lateral subungual onychomycosis in which the fungi infect the nail via the skin and directly invade the nail plate. Total dystrophic onychomycosis involves the entire nail unit (see the image below).

Distal subungual onychomycosis. Onycholysis and yeDistal subungual onychomycosis. Onycholysis and yellow streak. Image courtesy of Dr Antonella Tosti.

Nail invasion by Candida is not common because the yeast needs an altered immune response as a predisposing factor to be able to penetrate the nails. Despite the frequent isolation of Candida from the proximal nail fold or the subungual space of patients with chronic paronychia or onycholysis, in these patients Candida is only a secondary colonizer. In chronic mucocutaneous candidiasis, the yeast infects the nail plate and eventually the proximal and lateral nail folds.

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Epidemiology

Frequency

United States

The recent proliferation of fungal infections in the United States can be traced to the large immigration of dermatophytes, especially Trichophyton rubrum, from West Africa and Southeast Asia to North America and Europe.[2]

International

The incidence of onychomycosis has been reported to be 2-13% in North America.[3] A multicenter survey in Canada showed the prevalence of onychomycosis at 6.5%.[4] Onychomycosis accounts for half of all nail disorders, and onychomycosis is the most common nail disease in adults. Toenails are much more likely to be infected than fingernails. Thirty percent of patients with a cutaneous fungal infection also have onychomycosis. The incidence of onychomycosis has been increasing, owing to such factors as diabetes, immunosuppression, and increasing age.[2]

Studies in the United Kingdom, Spain, and Finland found prevalence rates of onychomycosis to be 3-8%.

Race

Onychomycosis affects persons of all races.

Sex

Onychomycosis affects males more commonly than females. However, candidal infections are more common in women than in men.

Age

Studies indicate that adults are 30 times more likely to have onychomycosis than children. Onychomycosis has been reported to occur in 2.6% of children younger than 18 years but as many as 90% of elderly people.

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Contributor Information and Disclosures
Author

Antonella Tosti, MD  Professor, Department of Dermatology, University of Bologna, Italy; Department of Dermatology & Cutaneous Surgery, Miller Medical School, University of Miami, Florida

Antonella Tosti, MD is a member of the following medical societies: American Academy of Dermatology, American Dermatological Association, Canadian Dermatology Association, European Academy of Dermatology and Venereology, International Society of Dermatology, and Women's Dermatologic Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Richard K Scher, MD  Professor of Dermatology, University of North Carolina

Richard K Scher, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Cryosurgery, American College of Physicians, American Dermatological Association, American Geriatrics Society, American Medical Association, Association of Military Surgeons of the US, International Society for Dermatologic Surgery, New York Academy of Sciences, Noah Worcester Dermatological Society, Rhode Island Medical Society, and Society for Investigative Dermatology

Disclosure: Nothing to disclose.

Richard P Vinson, MD  Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA

Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association

Disclosure: Nothing to disclose.

Jeffrey Meffert, MD  Assistant Clinical Professor of Dermatology, University of Texas Health Science Center-San Antonio

Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, and Texas Dermatological Society

Disclosure: Nothing to disclose.

Catherine M Quirk, MD  Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania

Catherine M Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology

Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD  Director, Department of Dermatology, Geisinger Medical Center

Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

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Distal subungual onychomycosis. Onycholysis and yellow streak. Image courtesy of Dr Antonella Tosti.
Distal subungual onychomycosis. Subungual hyperkeratosis onycholysis and yellow streak. Image courtesy of Dr Antonella Tosti.
Proximal subungual onychomycosis. Proximal leukonychia. Image courtesy of Dr Antonella Tosti.
White superficial onychomycosis. Image courtesy of Dr Antonella Tosti.
Candidal onychomycosis in a patient with chronic mucocutaneous candidiasis. Total onychomycosis and paronychia. Image courtesy of Dr Antonella Tosti.
 
 
 
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