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Onychomycosis, also known as tinea unguium, is a fungal infection of the nail. It primarily affects toenails but can also impact fingernails.

This condition manifests as white or yellow discolouration, thickening of the nail, and in severe cases, separation of the nail from the nail bed. Onychomycosis can lead to complications such as lower leg cellulitis and is more common in older males.

The condition is caused by various fungi, including dermatophytes and Fusarium, and it frequently recurs after treatment.

A toenail affected by onychomycosis
A toenail affected by onychomycosis

The most common symptom of onychomycosis is the thickening and discolouration of the nail, which can appear white, black, yellow, or green. As the infection progresses, the nail may become brittle and fragment, potentially detaching from the nail bed. Untreated infections can lead to inflammation and pain in the surrounding skin, white or yellow patches on the nailbed, scaly skin adjacent to the nail, and a foul odour. Although the condition is usually painless, severe cases can cause discomfort. Psychosocial issues may arise due to the nail's unsightly appearance, especially if fingernails are affected.

A case of fungal infection of the big toe
A case of fungal infection of the big toe
Advanced fungal infection of the big toe
Advanced fungal infection of the big toe

Onychomycosis is caused by fungi, including dermatophytes, Candida (yeasts), and nondermatophytic moulds. Dermatophytes are the primary cause in temperate regions, while Candida and nondermatophytic moulds are more common in tropical and subtropical climates. Trichophyton rubrum is the most prevalent dermatophyte causing the condition.

Other causative agents include Candida species, which primarily cause fingernail infections in individuals who frequently immerse their hands in water, and nondermatophytic moulds like Scytalidium, Scopulariopsis, and Aspergillus.

Risk factors for onychomycosis include advanced age, male gender, a family history of the condition, heavy perspiration, humid environments, wearing non-ventilated footwear, and walking barefoot in damp public places. Conditions such as diabetes, peripheral vascular disease, psoriasis, and a weakened immune system also increase susceptibility.

Diagnosis is generally based on appearance and confirmed through laboratory testing, including potassium hydroxide smear, culture, histology examination, and polymerase chain reaction. Nail scrapings or clippings from the affected area are typically examined.

Onychomycosis can be classified into five types:

  • Distal subungual onychomycosis
  • White superficial onychomycosis (WSO)
  • Proximal subungual onychomycosis
  • Endonyx onychomycosis
  • Candidal onychomycosis

Conditions that can be confused with onychomycosis include psoriasis, chronic dermatitis, chronic paronychia, nail trauma, green nail syndrome, yellow nail syndrome, and normal ageing.

A person's foot with a fungal nail infection ten weeks into a course of terbinafine oral medication. Note the band of healthy (pink) nail growth behind the remaining infected nails.
A person's foot with a fungal nail infection ten weeks into a course of terbinafine oral medication. Note the band of healthy (pink) nail growth behind the remaining infected nails.

Antifungal treatments can be topical or oral. Oral terbinafine is the most effective but has potential side effects, such as liver issues. Topical treatments include ciclopirox nail paint, amorolfine, and efinaconazole, though these are less effective and require prolonged use. Efinaconazole has shown better cure rates than other topical treatments.

Chemical or surgical debridement of the affected nail can enhance outcomes. Laser treatment is under investigation, and tea tree oil is not recommended due to skin irritation.

In the United States, the cost of terbinafine treatment is relatively low, whereas efinaconazole is expensive unless drug coupons are used. In Canada, efinaconazole treatment costs vary, with a 48-week course estimated at $178 for a big toe.

Recurrence is common, with a 20-25% relapse rate within two years. Onychomycosis can cause permanent nail damage and serious infections in immunocompromised individuals, particularly those with diabetes.

Onychomycosis is the most frequent fungal foot infection in Europe, with a prevalence of 27%. In Canada, the prevalence is estimated at 6.48%. It affects about one-third of diabetics and is more common in individuals with psoriasis.

The term "onychomycosis" is derived from Ancient Greek, with "onyx" meaning nail, "mykēs" meaning fungus, and the suffix "-osis" indicating a functional disease.

Research is ongoing into the efficacy of laser treatment and photodynamic therapy, which may offer future advancements in treating onychomycosis.

Self-assessment MCQs (single best answer)

What is another name for onychomycosis?

What is the most common symptom of onychomycosis?

Which of the following is the most prevalent dermatophyte causing onychomycosis?

Which of the following is NOT a risk factor for onychomycosis?

Which type of onychomycosis is characterised by white patches on the surface of the nail?

Which of the following is the most effective oral antifungal treatment for onychomycosis?

What is a common side effect of oral terbinafine?

Which laboratory test is NOT used to diagnose onychomycosis?

What is the estimated prevalence of onychomycosis in Europe?

Which treatment is currently under investigation and not yet established for onychomycosis?


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