What is the recommended diagnosis and management for onychomycosis of the toenail?

Management of Fungal Toenail Infection (Onychomycosis)

Do not treat fungal toenail infection based on clinical appearance alone—always confirm the diagnosis with laboratory testing (KOH preparation, fungal culture, or nail biopsy) before starting therapy, as 50% of nail dystrophy is non-fungal and treatment failure most commonly results from incorrect diagnosis. 1, 2

Diagnostic Approach

Laboratory Confirmation Required

• Obtain subungual debris from the most proximal part of the infection using a dental scraper to scrape beneath the nail or from the underside if the nail is onycholytic 1
• Submit material for both direct microscopy with 20% potassium hydroxide (visualizes fungal elements) and fungal culture on Sabouraud's glucose agar (identifies species) 1
• Culture plates must be incubated at 28°C for at least 3 weeks before declaring negative, as dermatophytes grow slowly 1
• For superficial white onychomycosis, scrape the surface of the infected nail plate with a curette 1

Key Diagnostic Pitfalls

• Clinical diagnosis alone leads to the most common cause of treatment failure in the U.K. 1
• Approximately 50% of nail dystrophy cases are non-fungal (psoriasis, trauma, lichen planus, bacterial infection) 1
• Bacterial infection (especially Pseudomonas aeruginosa) causes green or black discoloration, not the soft friable surface typical of fungal infection 1

First-Line Treatment

Oral terbinafine 250 mg daily for 12 weeks is the gold standard for dermatophyte toenail onychomycosis, achieving approximately 73% mycological cure rates at 48 weeks post-treatment. 3, 2

Why Terbinafine is Preferred

• Superior mycological and clinical cure rates compared to other systemic agents 3
• Low risk of drug interactions and hypoglycemia, making it particularly preferred in diabetic patients 3
• Better cost-effectiveness than alternatives 4
• FDA-approved specifically for onychomycosis of the toenail 2

Monitoring Requirements

• Obtain baseline liver function tests and complete blood count before initiating therapy 5
• Monitor for reversible taste disturbance and idiosyncratic liver reactions 3
• Hepatic function testing is recommended in patients with pre-existing liver abnormalities 3
• Be aware of drug-drug interactions with tricyclic antidepressants, SSRIs, atypical antipsychotics, beta blockers, or tamoxifen 6

Second-Line Treatment

If terbinafine is contraindicated or has failed, use itraconazole 200 mg daily for 12 weeks continuously, or pulse therapy at 400 mg daily for 1 week per month for 3 pulses. 3

Itraconazole Considerations

• Pulse therapy offers better compliance but slightly lower efficacy than continuous dosing 3
• Contraindicated in heart failure due to negative inotropic effects 3
• More effective than terbinafine for non-dermatophyte mold infections (e.g., Scopulariopsis), achieving approximately 88% cure rate 3
• Broad-spectrum activity against dermatophytes, yeasts, and some non-dermatophytic molds 4

Topical Therapy

Reserve topical agents for mild-to-moderate disease affecting only the distal nail without lunula involvement, or when systemic therapy is contraindicated. 3

Topical Options

• Amorolfine 5% nail lacquer shows approximately 50% efficacy when only distal nail portions are infected 3
• Efinaconazole 10% achieves mycological cure rates approaching 50% with complete cure in 15% after 48 weeks 3
• Ciclopirox 8% and tavaborole 5% are alternatives with fewer adverse effects and drug interactions than oral agents 6
• Combining topical with systemic therapy creates antimicrobial synergy, broadens spectrum, improves cure rates, and suppresses resistant strains 3

Critical Treatment Considerations

Factors Predicting Treatment Failure

• Nail thickness >2 mm significantly reduces treatment success 3
• Severe onycholysis predicts poor outcomes 3
• Dermatophytomas (dense white hyphal masses beneath the nail) require mechanical removal before antifungal therapy can be effective 3
• Slow nail outgrowth is associated with treatment failure 3

Mechanical Debridement

• Debride all infected keratin as the first step to reduce fungal load 4
• Nail trimming and debridement used concurrently with pharmacologic therapy improve treatment response 6
• Dermatophytomas must be mechanically removed, then followed by systemic antifungal treatment 3

Timeline and Expectations

Complete toenail regrowth requires up to 18 months due to slow growth patterns—maintaining a fungus-free status throughout this period is critical for success. 3, 5

• Toenails take approximately 12 months to grow out completely 1
• This is far too long to await results of a therapeutic trial, which is why laboratory confirmation before treatment is essential 1
• Therapeutic success is confirmed when the newly grown nail plate is free of fungal elements 3

Preventing Recurrence

Onychomycosis exhibits a 40-70% recurrence rate, making post-treatment prophylaxis essential. 3

Evidence-Based Prevention Strategies

• Discard old contaminated footwear or decontaminate shoes with naphthalene mothballs for three days 3, 5
• Apply antifungal powders (miconazole, clotrimazole, or tolnaftate) inside shoes and on feet regularly 3, 5
• Wear protective footwear in public bathing facilities, gyms, and hotel rooms where T. rubrum is commonly found 3, 5
• Wear cotton, absorbent socks and change them daily 5
• Keep toenails trimmed short and avoid sharing nail clippers 5
• Treat all infected household members simultaneously to decrease recurrence 3

Special Populations

Diabetic Patients

• Terbinafine is the preferred treatment due to lower cardiovascular risk and minimal drug interactions 3
• Onychomycosis in elderly diabetic patients can lead to cellulitis and further compromise limbs with peripheral vascular disease 1

Immunosuppressed Patients

• Terbinafine or fluconazole are preferred due to reduced antiretroviral drug interactions 3

Pediatric Patients

• Children experience higher cure rates (approximately 94-100%) and faster therapeutic response compared with adults 3

When Systemic Therapy is Contraindicated

• Consider topical monotherapy for mild to moderate onychomycosis 7
• Laser therapy (Nd:YAG) might be appropriate for patients with hepatic impairment or heart failure, though the British Association of Dermatologists states evidence is insufficient for standard recommendation 3
• Surgical avulsion followed by topical therapy alone "cannot be generally recommended" due to only 56% mycological cure and high recurrence rates 3
• If surgical excision has already been performed, systemic antifungal therapy must be initiated to eradicate residual fungal elements in the nail bed and prevent recurrence 3