Snapshot A 7-year-old boy presents to his pediatrician’s office for a white rash on his nails. His mom reports that he has a history of tinea pedis and tinea manuum and thought that this might be related. On physical exam, his left fourth and fifth finger have a thin, white, and powder-like discoloration of the nail plate. He is given topical therapy for this rash. 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 due to Trichophyton rubrum superficial white onychomycosis common in children affects surface of nail plate due to Trichophyton mentagrophytes proximal subungual onychomycosis uncommon usually in immunocompromised patients affects proximal nail plate due to Trichophyton rubrum Associated conditions tinea pedis tinea cruris Epidemiology Prevalence 3% prevalence in adults 20% prevalence in adults > 60 years old Demographics male > female adults > 60 years old Location toenails > fingernails Risk factors moist and warm environment increasing age immunosuppression occlusive shoes communal baths Etiology Pathogenesis fungal infection of keratinized tissue of nail plate Dermatophytes Trichophyton most commonly Trichophyton rubrum Microsporum Epidermophyton Candida spp. less common cause of onychomycosis Presentation Symptoms asymptomatic Physical exam distal and lateral or proximal subungual onychomycosis thickened with white, yellow, or brown discoloration thickened nail may separate from nail bed (onycholysis) 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 performed 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 itraconazole for dermatophytes and Candida spp. Operative nail avulsion indication severe onycholysis, thickening, or dermatophytomas Complications Secondary bacterial infection Prognosis High rates of recurrence