Toenail Fungus

Onychomycosis (also known as “Dermatophytic onychomycosis,” ”Ringworm of the nail,” ”Tinea unguium” Toenail Fungus) means fungal infection of the nail.  It is the most common disease of the nails and constitutes about a half of all nail abnormalities.

This condition may affect toenails or fingernails, but toenail infections are particularly common. The prevalence of onychomycosis is about 6-8% in the adult population.

Classification

There are four classic types of onychomycosis:

Distal subungual onychomycosis

The most common form of tinea unguium usually caused by Trichophyton rubrum, which invades the nail bed and the underside of the nail plate.

White superficial onychomycosis

Caused by fungal invasion of the superficial layers of the nail plate to form “white islands” on the plate. Accounts for only 10 percent of onychomycosis cases. In some cases, WSO is a misdiagnosis of “Keratin Granulations” which are not a fungus, but a reaction to nail polish that can cause the nails to have a chalky white appearance. A laboratory test should be performed to confirm.

Proximal subungual onychomycosis

Fungal penetration of the newly formed nail plate through the proximal nail fold. It is the least common form of tinea unguium in healthy people but found more commonly when the patient is immunocompromised.

Candidal onychomycosis

Candida species invade fingernails usually occurring in persons who frequently immerse their hands in water. This normally requires the prior damage of the nail by infection or trauma.

Signs and symptoms

The nail plate can have a thickened, yellow, or cloudy appearance. The nails can become rough and crumbly, or can separate from the nail bed. There is usually no pain or other bodily symptoms, unless the disease is severe.

Dermatophytids are fungus-free skin lesions that sometimes form as a result of a fungus infection in another part of the body. This could take the form of a rash or itch in an area of the body that is not infected with the fungus. Dermatophytids can be thought of as an allergic reaction to the fungus.

Patients with onychomycosis may experience significant psychosocial problems due to the appearance of the nail. This is particularly increased when fingernails are affected.

Causes

The causative pathogens of onychomycosis include dermatophytes, Candida, and non-dermatophytic molds. Dermatophytes are the fungi most commonly responsible for onychomycosis in the temperate western countries; meanwhile, Candida and non-dermatophytic molds are more frequently involved in the tropics and subtropics with a hot and humid climate.

Dermatophytes

Trichophyton rubrum is the most common dermatophyte involved in onychomycosis. Other dermatophytes that may be involved are Trichophyton interdigitale,Epidermophyton floccosum, Trichophyton violaceum, Microsporum gypseum, Trichophyton tonsurans, Trichophyton soudanense (considered by some to be an African variant of T. rubrum rather than a full-fledged separate species) and the cattle ringworm fungus Trichophyton verrucosum. A common outdated name that may still be reported by medical laboratories is Trichophyton mentagrophytes for T. interdigitale. The name T. mentagrophytes is now restricted to the agent of favus skin infection of the mouse; though this fungus may be transmitted frommice and their danders to humans, it generally infects skin and not nails.

Other

Other causative pathogens include Candida and non-dermatophytic moulds, in particular members of the mould generation Scytalidium (name recently changed to Neoscytalidium), Scopulariopsis, and Aspergillus.Candida mainly cause fingernail onychomycosis in people whose hands are often submerged in water. Scytalidium mainly affects people in the tropics, though it persists if they later move to areas of temperate climate.

Other molds more commonly affect people older than 60 years, and their presence in the nail reflects a slight weakening in the nail’s ability to defend itself against fungal invasion.

Risk factors

Risk factors for onychomycosis include family history, increasing age, poor health, prior trauma, warm climate, participation in fitness activities, immunosuppression (e.g., HIV, drug induced), communal bathing, and occlusive footwear.

Diagnosis

To avoid misdiagnosis as nail psoriasis, lichen planus, contact dermatitis, trauma, nail bed tumor or yellow nail syndrome, laboratory confirmation may be necessary. The three main approaches are potassium hydroxide smear, culture and histology. This involves microscopic examination and culture of nail scrapings or clippings. Recent results indicate that the most sensitive diagnostic approaches are direct smear combined with histological examination, and nail plate biopsy using periodic acid-Schiff stain.  To reliably identify nondermatophyte molds several samples may be necessary.