Onychomycosis

(Tinea Unguium)

ByChris G. Adigun, MD, Dermatology & Laser Center of Chapel Hill
Reviewed/Revised Dec 2021
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(See also Overview of Nail Disorders.)

About 10% (range 2 to 14%) of the population has onychomycosis.

Risk factors for onychomycosis 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.

Onychomycosis
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Onychomycosis is fungal infection of the nail plate, nail bed, or both. Infection may be distal subungual, with nail thickening and yellowing and accumulation of keratin and debris underneath the nail (top); proximal subungual (not pictured); or white superficial, with spreading of chalky white scale beneath the nail surface (bottom).
Images provided by Thomas Habif, MD.

Symptoms and Signs

Nails have asymptomatic patches of white or yellow discoloration and deformity. There are 3 common characteristic patterns:

  • Distal subungual: The nails thicken and yellow, keratin and debris accumulate distally and underneath, and the nail separates from the nail bed (onycholysis).

  • Proximal subungual: A form that starts proximally and is a marker of immunosuppression.

  • White superficial: A chalky white scale slowly spreads beneath the nail surface.

Onychomycosis of the Great Toes
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This photo shows onychomycosis of the great toenails. The right toenail shows classic distolateral (a distal subungual) onychomycosis (DLO), whereas the left toenail likely began as DLO and progressed to dermatophytoma (dense collection of hyphae that appears as a linear streak).
Image courtesy of Dr. Edwin P. Ewing, Jr. via the Public Health Image Library of the Centers for Disease Control and Prevention.

Diagnosis

  • Clinical evaluation

  • Potassium hydroxide wet mount examination

  • Culture or polymerase chain reaction (PCR)

  • Histopathologic examination of periodic acid-Schiff (PAS)–stained nail clippings and subungual debris

(See also an update on the current approaches to diagnosis and treatment of onychomycosis.)

Onychomycosis is suspected by appearance in patients who also have tinea pedis; 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 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. Although more expensive, PCR has become a more common technique to confirm the diagnosis of onychomycosis, especially if cultures are negative or a definitive diagnosis is required (1, 2, 3). Histopathologic examination of PAS–stained nail clippings and subungual debris may also be helpful.

Obtaining an adequate sample of nail for culture 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.

Diagnosis references

  1. 1. Joyce A, Gupta AK, Koenig L, et al: Fungal Diversity and Onychomycosis: An analysis of 8,816 toenail samples using quantitative PCR and next-generation sequencing. J Am Podiatr Med Assoc 109(1):57–63, 2019. doi: 10.7547/17-070

  2. 2. Haghani I, Shams-Ghahfarokhi M, Dalimi Asl A, et al: Molecular identification and antifungal susceptibility of clinical fungal isolates from onychomycosis (uncommon and emerging species). Mycoses 62(2):128–143, 2019. doi: 10.1111/myc.12854

  3. 3. Gupta AK, Mays RR, Versteeg SG, et al: Update on current approaches to diagnosis and treatment of onychomycosis. Expert Rev Anti Infect Ther 16(12):929–938, 2018. doi: 10.1080/14787210.2018.1544891

Treatment

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:

  • Previous ipsilateral cellulitis

  • Diabetes or other risk factors for cellulitis

  • Presence of bothersome symptoms

  • Psychosocial impact

  • Desire for cosmetic improvement (controversial)

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.

Key Points

  • Onychomycosis is highly prevalent, particularly among older men and patients with compromised distal circulation, nail dystrophies, and/or tinea pedis.

  • Suspect the diagnosis based on appearance and the pattern of nail involvement and confirm it by microscopy and culture or PCR.

  • Treatment is warranted only if onychomycosis causes complications or troublesome symptoms.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

  1. Update on current approaches to diagnosis and treatment of onychomycosis (2018)

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