Toenail Fungus (Onychomycosis): Diagnosis and Treatment
Confirm the Diagnosis Before Treatment
Do not treat based on appearance alone—mycological confirmation is mandatory before initiating antifungal therapy, as only 50% of dystrophic nails are actually fungal infections despite looking identical clinically. 1, 2
Essential Diagnostic Testing
Collect specimens properly: Scrape subungual debris from the most proximal part of the infection using a dental scraper, cutting through the entire thickness of the nail and including all crumbly material. 3, 2
Order both KOH preparation with microscopy AND fungal culture on Sabouraud's glucose agar (incubated at 28°C for at least 3 weeks) to identify the specific pathogen. 4, 3
Consider calcofluor white staining if initial testing is negative but clinical suspicion remains high—this enhances visualization of fungal elements and increases sensitivity significantly. 4, 2
If testing remains negative but suspicion is high, request PAS (periodic acid-Schiff) staining on nail clippings, which demonstrates 82-92% sensitivity compared to 48-80% for KOH and 53-59% for culture. 2
Clinical Features That Support Fungal Infection
Distal and lateral subungual onychomycosis (DLSO) is the most common presentation: thickened, discolored nails with subungual hyperkeratosis and onycholysis, nearly always accompanied by tinea pedis on examination. 1
Soft, friable nail texture strongly suggests fungal infection, whereas hard, brittle texture suggests non-infectious causes. 3, 2
Trichophyton rubrum causes over 90% of dermatophyte toenail infections. 1
First-Line Treatment: Oral Terbinafine
Oral terbinafine is the preferred first-line treatment for dermatophyte onychomycosis, with superior efficacy (76% mycotic cure rate) compared to all other systemic agents. 5, 6, 7
Dosing and Duration
250 mg daily for 12 weeks for toenails (6 weeks for fingernails). 5, 6
Weight-based dosing for children: <20 kg = 62.5 mg daily; 20-40 kg = 125 mg daily; >40 kg = 250 mg daily. 4
Monitoring Requirements
Baseline liver function tests and complete blood count are recommended before starting therapy. 4
Monitor for drug-drug interactions in patients taking tricyclic antidepressants, SSRIs, atypical antipsychotics, beta blockers, or tamoxifen. 6
Alternative Oral Therapy: Itraconazole
Itraconazole pulse therapy is equally effective as first-line treatment and particularly useful when Candida species are suspected (63% cure rate with pulse dosing). 4, 7
Dosing and Duration
Pulse therapy: 200 mg twice daily for 1 week per month (or 5 mg/kg/day for children). 4
3 pulses (3 months total) for toenails; 2 pulses (2 months total) for fingernails. 4
Monitor liver function tests for patients receiving continuous therapy >1 month or those with pre-existing hepatic abnormalities. 4
Topical Therapy: Limited Role
Topical antifungals have significantly lower cure rates (ciclopirox has >60% failure rate) and should be reserved for mild disease limited to the distal nail plate or when oral therapy is contraindicated. 8, 6, 7
FDA-Approved Topical Options
Efinaconazole 10% solution or tavaborole 5% solution have better efficacy than ciclopirox but still inferior to oral agents. 6, 9
Treatment duration is much longer (typically 48 weeks) compared to oral therapy. 10
Adjunctive Measures That Improve Outcomes
Nail trimming and debridement used concurrently with pharmacologic therapy significantly improve treatment response. 6, 7
Additional Recommendations
Apply regular antifungal powder inside shoes and periodically spray terbinafine solution into shoes to prevent reinfection. 4
Daily topical emollients to cuticles and periungual tissues help maintain nail health. 4, 3
Disinfect shoes and socks to reduce the 25% relapse rate. 6
Avoid walking barefoot in public places as a preventive measure. 6, 10
Critical Pitfalls to Avoid
Never assume fungal infection without laboratory confirmation—the cost of diagnostic testing is always small relative to inappropriate 12-month treatment courses. 2
Do not accept a single negative test as definitive—false negatives are common due to inadequate specimen collection; pursue enhanced testing methods if clinical suspicion remains high. 2
Recognize non-fungal mimics: Psoriasis (nail pitting, oil drop sign), lichen planus (nail thinning with dorsal pterygium), and traumatic onycholysis can all appear similar but require different management. 3, 2
Check for proximal subungual onychomycosis (PSO) in immunocompromised patients—this pattern is uncommon in the general population but common in HIV/AIDS patients and may indicate underlying immunosuppression. 1
Examine family members for fungal infections, as household transmission is common. 4