Onychomycosis - Nail and Distal Digit
Alerts and Notices
SynopsisOnychomycosis is a fungal infection of the nail (tinea unguium) caused by dermatophyte fungi and, less frequently, by nondermatophyte molds or yeasts. Onychomycosis is more frequent in men and is commonly associated with concurrent tinea pedis. The prevalence of onychomycosis in children varies from 0.2%-2.6% (mean 0.3%). The low prevalence in children compared with adults is thought to be due to children's fast nail plate growth and their lower incidence of tinea pedis compared with adults.
Predisposing factors include diabetes mellitus, peripheral vascular disease, immunosuppression, genetic predisposition, atopic dermatitis, psoriasis, Down syndrome, occlusive footwear, obesity, malignancy, trauma, and older age. Patients may also report a history of hyperhidrosis. A personal history of tinea pedis and/or contact with a household member with onychomycosis / tinea pedis are among the most common risk factors. Toenails are more commonly affected than fingernails, and fingernail infection is typically preceded by or associated with toenail infection. Onychomycosis is classified into 7 patterns based on the route of fungal invasion into the nail unit: distal lateral subungual, superficial, proximal subungual, endonyx, mixed pattern, totally dystrophic, and secondary onychomycosis.
Distal lateral subungual onychomycosis (DLSO) is the most common form of onychomycosis and begins with fungal invasion of the distal nail (hyponychium). In Western countries, DLSO is mainly due to Trichophyton rubrum.
Superficial onychomycosis (SO) is due to fungal invasion of the superficial dorsal nail plate, typically caused by T rubrum in HIV-infected patients and Trichophyton mentagrophytes in immunocompetent individuals. In children, superficial white onychomycosis (SWO) is typically caused by T rubrum. It accounts for 8%-28% of pediatric cases.
Proximal subungual onychomycosis (PSO) is caused by invasion of the proximal nail fold. In the absence of paronychia, PSO is typically due to T rubrum.
Endonyx onychomycosis (EO) presents as lamellar nail splitting and milky patches of the nail plate. The fungus directly invades the nail plate, but there is no penetration of the nail bed. The most common organisms are Trichophyton soudanense and Trichophyton violaceum.
Mixed pattern onychomycosis (MPO) occurs when there is more than one pattern of nail plate infection in the same nail. The most common patterns are PSO with SO or DLSO with SO.
Total dystrophic onychomycosis (TDO) presents as a crumbled nail plate and is the end stage of onychomycosis, typically DLSO.
Secondary onychomycosis occurs when fungi invade the nail plate secondary to other nonfungal nail diseases, such as psoriasis or prior trauma.
The dermatophytes T rubrum and T mentagrophytes are the first and second most common organisms in the United States. Other organisms include Microsporum canis and Trichophyton tonsurans.
Nondermatophyte molds are less commonly responsible for onychomycosis than dermatophytes. However, they are increasingly being recognized in warmer climates. Aspergillus, Acremonium, and Fusarium species and Scytalidium hyalinum may be responsible for DLSO, SO, and PSO; Scopulariopsis brevicaulis may present with brown-yellow nail plate discoloration; and Scytalidium dimidiatum typically presents with black nail discoloration.
When Candida species are cultured from nails, these species are not always the primary pathogen. Candida is commonly associated with chronic paronychia and occasionally secondarily infects the nail plate. True nail invasion by Candida is seen commonly in patients with chronic mucocutaneous candidiasis.
Immunocompromised Patient Considerations:
PSO has been reported to be more common in HIV infection and immunocompromised states.
Candida onychomycosis is seen in patients with chronic mucocutaneous candidiasis who are prone to direct invasion of Candida into their nail plate.
Infected nails may be the source of disseminated mycosis in immunosuppressed patients, especially those with hematologic malignancies or neutropenia.
Inherited deficiency (autosomal recessive) of CARD9 (caspase recruitment domain-containing protein 9), which is involved in the inflammatory cascade, may result in deep ulcerated fungal infections, Majocchi-like granulomas, severe tinea capitis and corporis, and onychomycosis. Other findings are high immunoglobulin E (IgE) antibody levels and lymphadenopathy, and eosinophilia. While uncommon, patients with these constellation of findings are found in North Africa (Tunisia, Algeria, Morocco). Trichophyton rubrum and T violaceum are the responsible organisms. The disease most often presents in children.
B35.1 – Tinea unguium
414941008 – Onychomycosis
Differential Diagnosis & Pitfalls
- Nail psoriasis – Multiple large, coarse, and deep pits randomly scattered on the nail plate; onycholysis (detachment of the nail plate from the nail bed) surrounded by an erythematous border; yellowish or salmon pink patches on the nail bed; subungual hyperkeratosis; and splinter hemorrhages.
- Trauma – Yellowing and thickening of the nail plate.
- Subungual wart – Thickening of the nail plate with subungual debris.
- Lichen planus – Thinning or ridging of the nail plate, dystrophic nail changes, and pterygium.
- Twenty-nail dystrophy, or trachyonychia – Characterized by rough nail surface with marked longitudinal striations resulting in splitting.
- Pachyonychia congenita – Marked subungual hyperkeratosis with accumulation of hard keratinous material resulting in uplifting of the nail plate.
- Amelanotic melanoma / subungual melanoma
- Squamous cell carcinoma
- Yellow nail syndrome
- Subungual exostoses
- Paronychia secondary to finger sucking or nail biting
Patient Information for Onychomycosis - Nail and Distal Digit
OverviewOnychomycosis, commonly known as a fungal nail infection, is infection of the fingernails or toenails by forms of fungi and yeast. Fungal nail infections account for nearly one-half of all nail disorders. In the most common form of fungal nail infections, fungus grows under the growing portion of the nail and spreads up the finger (proximally) along the nail bed and the grooves on the sides of the nails. A less common type of fungal nail infection may occur in those with HIV/AIDS.
Who’s At RiskFungal nail infection may occur at any age but is more common in adults, particularly in older individuals. Diabetics may be more likely than other people to develop a fungal nail infection.
Signs & Symptoms
- In general, toenails are most commonly affected with fungal nail infection. If the fingernails are affected, the toenails are usually affected as well. Nails often become thicker and lift from the nail bed (onycholysis) starting at the growing portion of the nail. You might then see debris under the nails and discoloration of the affected area.
- In some forms of fungal nail infection, you might see black or white, powdery discoloration on the surface of the nail plate.
- In some forms of fungal nail infection, you might see these abnormal changes farther up the finger (proximally), where the nail originates.
- Fungal nail infection may occur in people with athlete's foot (tinea pedis) and/or oozing infection (paronychia), caused by inflammation and infection with yeast and/or bacteria in the region where the skin of the finger meets the origin of the nail.
- In fungal nail infection, one, a few, or all nails may be affected.
- None necessary except good hygiene and regular washing of the hands and feet.
When to Seek Medical CareFungal nail infection does not always require treatment, but see your doctor for any nail disorder. Diabetics with foot problems should be evaluated because of the possible risk for developing foot ulcers. Your doctor may perform testing, such as scraping a nail to examine for fungi or clipping a nail to look for bacterial or fungal growth (culture) or to obtain a special stain to look for fungi under a microscope.
- Topical therapy with ciclopirox nail lacquer, which requires daily application for 9-12 months.
- Oral antifungal treatments offer the best chance for curing fungal nail infection. The most commonly used agents are terbinafine, itraconazole, and fluconazole. The medications may cause liver problems or may affect blood cell counts. Blood tests are usually performed before starting therapy and during therapy to look for possible side effects.
- In stubborn (refractory) fungal nail infection, surgical removal of part of the nail or the entire nail, removing the nail by applying a chemical, or thinning the nail by applying 40% urea ointment may be used, in addition topical or oral antifungal agents.
Bolognia, Jean L., ed. Dermatology, pp.1062, 1072. New York: Mosby, 2003.
Onychomycosis - Nail and Distal Digit