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Onychomycosis

Disease name and synonyms

Onychomycosis (tinea unguium, fungal infection of the nails, paronychia)

Fungi may affect the nail fold (paronychia) or the nail itself (onychomycosis)

Fungi responsible

Paronychia is usually caused by Candida albicans and occasionally other Candida species. Onychomycosis is caused by a wide variety of fungi especially T. rubrum, which causes about 80% of cases in the UK.  Non-dermatophyte moulds that occasionally cause onychomycosis, usually of the toenail, include Fusarium spp., Aspergillus spp., Acremonium spp., Alternaria alternata, Scytalidium dimidiatum, Scytalidium hyalinium (Nattrassia mangiferae), Scopulariopsis brevicaulis and Onychocola canadensis. C. albicans and, rarely, Candida parapsilosis cause onychomycosis, especially superficial white onychomycosis. Some infections are caused by more than one fungus.

Disease description

Toenails are more commonly affected than fingernails. Discolouration of the nail, either in part of completely is typical.

Frequency and global burden

Fungal nail infection (onychomycosis) is common in the general adult population, probably 5-25% rate with an increasing incidence in elderly people.

Underlying problems and at risk patients

Patients with AIDS may present with onychomycosis, especially superficial white onychomycosis. Candida paronychia is more common in those with extensive water contact with their hands. Onychomycosis caused by Fusarium spp. may lead to disseminated infection in leukaemia patients.

Diagnostic testing

Scraping of the nail itself, or the material under the nail is the most rewarding material. Microscopy and fungal culture. PCR for T. rubrum in some institutions.

Treatments

Candida paronychia, when mild and localized, will usually respond to imidazole or terbinafine cream or nystatin ointment applied topically for 1–3 weeks. Very localised distal nail infection may respond topical amorolfine or ciclopirox, but results are inferior to oral therapy. Oral therapy with terbinafine or itraconazole for many weeks or months is 80+% effective. Griseofuvin is over 80% effective for fingernail onychomycosis, but less than 40% effective for toenail disease. Topical amphotericin B in a 50:50 (v/v) mixture of dimethylsulphoxide and 2-propanol at a final concentration of 2 mg/ml may be effective for susceptible fungi such as Fusarium and Acremonium. 1-3 drops are applied daily and allowed to dry, for 12+ months. Urea-based cream allows softening of the nail and improved penetration of topical agents. Nail removal is sometimes necessary, and always so for infections caused by Scopulariopsis or Scytalidium.

Outlook and prognosis

Cure is possible, but takes a long time, as the growth of the nails is slow. .

British Association of Dermatologists' guidelines for the management of onychomycosis (2014)

Images

Patterns of onychomycosis (from Denning et al. Fungal nail disease: a guide to good practice. Br Med J 1995]

Onychomycosis of three fingernails caused by T. rubrum.

Bilateral onychomycosis caused by the non-dermatophyte allergenic brown mould Alternaria alternata.

A very typical example of lateral onychomycosis on the great toenail.

Superficial white onychomycosis, typically caused by T. interdigitale or C. albicans.

An example of chronic candida onychomycosis (part of the syndrome of chronic mucocutaneous candidiasis) showing a normal 5th fingernail, a hardened touch 4th fingernail, a completely destroyed 3rd fingernail and an infected and deformed index fingernail.

Another example of onychomycosis of the great toe, perhaps the commonest pattern

Onychomycosis in AIDS, with evidence of localised skin involvement as well.

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