Snapshot A 63-year-old woman presents to her physician's office reporting a bothersome nail. She reports that she has a rash on her right foot and on her right big toe. She noticed this a few weeks ago and had thought that it would self-resolve. However, she says that this rash has persisted. On physical exam, her right big toe nail is thickened and yellow. Adjacent to this are fissures and scales. KOH preparation of the scales show hyphae, indicating a fungal infection. Introduction Clinical definition a dermatophytosis superficial fungal infection of the nail involving nail bed and underside of nail plate also called tinea unguium types of onychomycosis distal and lateral subungual onychomycosis most common affects nail bed and underside of nail plate superficial white onychomycosis common in children affects surface of nail plate proximal subungual onychomycosis uncommon usually in immunocompromised patients affects proximal nail plate Epidemiology prevalence 3% prevalence in adults 20% prevalence in adults > 60 years of age demographics male > female adults > 60 years of age location toenails > fingernails risk factors moist and warm environment increasing age immunosuppression occlusive shoes communal baths Etiology dermatophytes Trichophyton most commonly Trichophyton rubrum Microsporum Epidermophyton Candida spp. less common cause of onychomycosis Pathogenesis fungal infection of keratinized tissue of nail plate Associated conditions tinea pedis tinea cruris Prognosis high rates of recurrence Presentation Symptoms asymptomatic Physical exam distal and lateral or proximal subungual onychomycosis thickened with white, yellow, or brown discoloration thickened nail may separate from the nail bed most commonly affects first or fifth nail superficial white onychomycosis white discoloration of nail plate powder-like Studies KOH preparation skin scrapings at active edge of lesion mixed with KOH presence of septated hyphae and spores indicates fungal infection Calcofluor white staining presence of branching hyphae Fungal culture if confirmation is needed or if KOH or calcofluor testing is negative Making the diagnosis usually based on clinical history and physical exam but confirmation with the aforementioned tests are recommended Differential Bacterial infection green or black discoloration may indicate Pseudomonas aeruginosa infection Psoriasis Trauma Treatment Medical topical therapy indications when there is < 80% nail involvement and no involvement of the lunula drugs efinaconazole 10% tavaborole 5% oral therapy indications involvement of lunula proximal subungual onychomycosis lack of response to topical therapy Candida onychomycosis drugs terbinafine for dermatophytes griseofulvin deposits in nails itraconazole for dermatophytes and Candida spp. Operative nail avulsion indications severe onycholysis, thickening, or dermatophytomas Complications Secondary bacterial infection