Fast Five Quiz: Fingernail and Toenail Conditions

William James, MD


February 07, 2020

Onychomycosis is caused by three main classes of fungi: dermatophytes, yeasts, and nondermatophyte molds. Dermatophytes are by far the most common cause of onychomycosis. Two major pathogens are responsible for the vast majority of onychomycosis cases. Trichophyton rubrum is the most common cause, with Trichophyton mentagrophytes the second-leading cause. Onychomycosis due to Candida is rare.

The subtypes of onychomycosis may be distinguished on the basis of their usual presenting clinical features. In distal lateral subungual onychomycosis, the nail shows subungual hyperkeratosis and onycholysis, which is usually yellow-white in color. Yellow streaks and/or yellow onycholytic areas in the central portion of the nail plate are commonly observed. Endonyx onychomycosis presents as a milky-white discoloration of the nail plate, but in contrast to distal lateral subungual onychomycosis, no evidence of subungual hyperkeratosis or onycholysis is present.

The clinical features of onychomycosis may mimic a large number of other nail disorders. Therefore, laboratory diagnosis of onychomycosis is recommended to be confirmed before beginning a treatment regimen. A negative mycologic result does not rule out onychomycosis. Direct microscopy cannot identify the specific pathogen involved in onychomycosis. A fungal culture is recommended to be used to identify the species of organism.

According to evidence-based guidelines for the management of onychomycosis from the British Association of Dermatologists, systemic treatment recommendations in adults are as follows:

  • Terbinafine is recommended as first-line treatment for dermatophyte onychomycosis and is generally preferred over itraconazole. It is not recommended for patients with active or chronic liver disease.

  • Fluconazole may be a useful alternative in patients unable to tolerate terbinafine or itraconazole.

  • Griseofulvin is no longer a treatment of choice, owing to lower efficacy and higher relapse rates compared with terbinafine and itraconazole.

  • Combination treatment is recommended if response to topical monotherapy is likely to be poor.

Adult topical treatment recommendations are as follows:

  • Amorolfine or tioconazole is useful for superficial and distal onychomycosis.

  • Ciclopirox is useful for superficial and distal onychomycosis and for patients in whom systemic therapy is contraindicated.

Read more about onychomycosis.


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