Onychomycosis
Onychomycosis is a dermatophyte infection of the nail, most often distal subungual disease of the toenails, causing yellow, white, or brown nail-plate discoloration, thickening, subungual debris, and onycholysis. Confirm with a potassium hydroxide preparation, periodic acid-Schiff stain, or fungal culture before treating, then use oral terbinafine 250 mg once daily for 6 weeks (fingernails) or 12 weeks (toenails), since topical agents alone rarely clear infection under the nail plate.
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What this article covers
- Overview
Definition: onychomycosis is a dermatophyte infection of the nail unit, most commonly the toenails, in which the fungal organism invades the nail bed and plate rather than only the surrounding skin.
- Epidemiology
Toenails more than fingernails: the toenail is the most commonly affected site, unlike nail psoriasis, which more commonly affects the fingernails.
- Risk factors
Older age. Diabetes mellitus. Peripheral vascular disease.
- Pathophysiology
Dermatophyte invasion of the nail unit: the organism, usually the same dermatophyte responsible for tinea pedis, invades the nail bed and plate rather than remaining confined to adjacent skin.
- Clinical features
Establishing features: a discolored (yellow, white, or brown), thickened distal nail plate with underlying subungual debris and separation of the plate from the nail bed (onycholysis) defines distal…
- Differential diagnosis
Nail psoriasis: pitting, oil-drop discoloration, onycholysis, subungual hyperkeratosis, and nail plate crumbling, distinguished because nail pitting is not seen in onychomycosis but is a clue to…
- Diagnosis
The diagnostic basis is laboratory confirmation of fungal invasion, not appearance alone: a discolored, thickened nail plate with subungual debris and onycholysis suggests onychomycosis, but…
- Management
First, confirm the fungal diagnosis before treating, since onychomycosis is treated mostly for cosmetic reasons and topical agents are of limited efficacy, so committing a patient to a lengthy course…
- Complications
Onycholysis and permanent nail-plate dystrophy from chronic untreated infection.
- Prognosis
Slow visible improvement even with effective therapy: clearing takes months because a healthy nail must grow out to replace the infected plate.
- Prevention
Treat concomitant tinea pedis with terbinafine 1% cream applied twice daily for 1 week for interdigital disease or twice daily for 2 weeks for plantar or lateral-foot disease to eliminate the reservoir that reinfects the nail.
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