How should I manage a 7‑month‑old infant with suspected onychomycosis of the toenail?

Management of Toenail Fungus in a 7-Month-Old Infant

Confirm the Diagnosis First

Before initiating any treatment in this infant, you must obtain mycological confirmation through potassium hydroxide (KOH) preparation with microscopy and/or fungal culture, as approximately 50% of nail dystrophies in children are non-fungal despite similar clinical appearance. 1, 2, 3

• Direct microscopy with KOH and fungal culture on Sabouraud's glucose agar are essential to avoid treating non-fungal conditions that can mimic onychomycosis 3
• Calcofluor white staining can enhance visualization of fungal elements if available 3
• Do not diagnose based on appearance alone—many conditions including psoriasis, lichen planus, trauma, and bacterial infections can present similarly 4, 3

Examine the Entire Family Unit

• Check the infant for concomitant tinea capitis and examine parents and siblings for onychomycosis and tinea pedis, as household transmission is extremely common 1, 2, 3
• Family members often serve as the source of infection in pediatric cases 2, 5

Treatment Approach for Confirmed Onychomycosis

Systemic Therapy (First-Line)

If onychomycosis is confirmed, oral terbinafine is the preferred first-line treatment, dosed at 62.5 mg daily for 12 weeks for toenails in infants weighing less than 20 kg. 1, 2

• Terbinafine demonstrates superior efficacy with an 88% cure rate in children aged 4-17 years 1, 2
• Baseline liver function tests and complete blood count are recommended before starting terbinafine 2
• Common adverse effects include headache, taste disturbance, and gastrointestinal upset 2
• Note that terbinafine is used off-label in this age group, as it is unlicensed for children 2, 5

Alternative Systemic Option

• Itraconazole pulse therapy (5 mg/kg/day for 1 week per month for 3 months total) is an equally effective alternative, particularly if Candida species are suspected 1, 2
• Itraconazole shows 94-100% clinical cure rates in pediatric studies 3

Concurrent Topical Therapy

Combine systemic treatment with topical antifungal therapy for any associated foot infection (tinea pedis). 1, 2

• Topical agents such as clotrimazole, ciclopirox, or amorolfine should be applied to affected skin 1
• Children respond better to topical therapy than adults due to thinner, faster-growing nails 2, 5
• However, ciclopirox 8% nail lacquer is only FDA-approved for children ≥12 years, so its use in a 7-month-old would be off-label 6, 5

Prevention Strategies (Implement Immediately)

• Decontaminate or replace contaminated footwear 1
• Apply antifungal powders (containing miconazole, clotrimazole, or tolnaftate) inside shoes regularly 1, 2
• Keep nails short and clean 1
• Avoid sharing nail clippers with infected family members 1, 2

Important Clinical Considerations

Why This Age Group Is Unusual

• Onychomycosis is rare in infants and young children, with a worldwide prevalence of only approximately 0.3% in the pediatric population 7, 8
• The increasing incidence in recent years suggests environmental or familial transmission 5, 9

Expected Clinical Pattern

• If confirmed as fungal, the most likely pattern is superficial white onychomycosis (SWO), which appears as crumbling white lesions on the nail surface and is most commonly seen in children, usually caused by T. interdigitale 4, 3
• Trichophyton rubrum is the most prevalent causative organism overall (64% of pediatric cases) 3, 8

Monitoring Requirements

• Monitor for at least 48 weeks from treatment start to identify potential relapse 1
• Children show faster response to antifungal therapy than adults 2

Common Pitfalls to Avoid

• Never assume fungal infection without laboratory confirmation—50% of dystrophic nails are non-fungal 3
• Do not overlook examination of family members, as household transmission is the primary source in pediatric cases 3
• Avoid concomitant use of topical ciclopirox nail lacquer with systemic antifungals, as no studies have determined whether this combination is safe or effective 6