Proximal Subungual Onychomycosis in Pediatric Patients
For proximal subungual onychomycosis (PSO) in a pediatric patient, obtain mycological confirmation via KOH preparation and fungal culture from subungual debris scraped from the proximal nail area before initiating treatment, then start oral terbinafine as first-line therapy using weight-based dosing: 62.5 mg daily for <20 kg, 125 mg daily for 20-40 kg, or 250 mg daily for >40 kg, given for 6 weeks for fingernails or 12 weeks for toenails. 1, 2, 3
Critical Diagnostic Approach
Why Confirmation is Mandatory
Never treat on clinical grounds alone, as only 50% of nail dystrophies are fungal in origin, and treatment requires 6-12 months to assess success—far too long to wait for a therapeutic trial. 1
The most common cause of treatment failure is incorrect initial diagnosis made without laboratory confirmation. 1
Specimen Collection for PSO
Scrape subungual debris from the most proximal part of the infection using a scalpel blade, as PSO is rare and requires sampling from the proximal nail area. 1
If standard scraping is inadequate, punch biopsy of the full-thickness nail plate with nail bed may be necessary to obtain diagnostic material. 1
Submit as much material as possible to the laboratory, as fungal elements are often scanty in nail specimens. 1
Laboratory Processing
KOH preparation with microscopy: Place specimen on glass slide with 20% potassium hydroxide, wait 15-20 minutes, then examine for fungal elements (hyphae). 1
Fungal culture on Sabouraud's glucose agar with antibiotics, incubated at 28°C for at least 3 weeks before declaring negative, as dermatophytes grow slowly. 1
Culture identifies the specific organism—critical because PSO is typically caused by Trichophyton rubrum in dermatophyte cases. 1
Red Flag: Immunosuppression Screening
PSO without paronychia is uncommon in immunocompetent children and should prompt evaluation for underlying immunosuppression. 1
PSO is a marker of HIV infection when caused by T. rubrum, though it can occur in other immunosuppressed states. 1
Check for conditions such as HIV, diabetes, peripheral vascular disease, or immunosuppressive medications (e.g., TNF-α inhibitors). 1, 4
In HIV-positive patients, PSO often spreads rapidly from the proximal margin to produce gross white discoloration without obvious thickening. 1
First-Line Treatment: Oral Terbinafine
Weight-Based Dosing
| Weight | Daily Dose | Fingernail Duration | Toenail Duration |
|---|---|---|---|
| <20 kg | 62.5 mg | 6 weeks | 12 weeks |
| 20-40 kg | 125 mg | 6 weeks | 12 weeks |
| >40 kg | 250 mg | 6 weeks | 12 weeks |
Why Terbinafine is Preferred
Superior efficacy: Adult data show 46% long-term mycological cure with terbinafine versus 13% with itraconazole, with lower relapse rates (23% vs 53%). 2
Better tolerability compared to itraconazole, though both are listed as first-line options with equal strength of recommendation. 2
Children achieve higher cure rates and faster responses than adults due to thinner nail plates (better drug penetration) and faster nail growth. 2
Pre-Treatment Requirements
Obtain baseline liver function tests (ALT, AST) and complete blood count before starting terbinafine, as it is unlicensed for pediatric use. 2, 3
Confirm diagnosis with mycological testing (KOH and culture) before initiating therapy. 3
Common Adverse Effects to Counsel
Headache and gastrointestinal upset (most frequent). 2
Taste disturbance (dysgeusia), which can be permanent in rare cases. 2
Rash, pruritus, urticaria. 2
Potential exacerbation of psoriasis or sub-acute lupus-like syndrome. 2
Alternative First-Line: Itraconazole Pulse Therapy
If terbinafine is contraindicated or not tolerated, use itraconazole 5 mg/kg per day for 1 week per month: 2 pulses (2 months total) for fingernails or 3 pulses (3 months total) for toenails. 2
Take with food in an acidic gastric environment to optimize absorption. 2
Monitor hepatic function in patients with pre-existing liver abnormalities or when continuous therapy exceeds one month. 2
Second-Line Options (When Both First-Line Agents Fail)
| Agent | Dose | Duration | Key Limitations |
|---|---|---|---|
| Fluconazole | 3-6 mg/kg once weekly | 12-16 weeks (fingernails) or 18-26 weeks (toenails) | Requires baseline LFTs and CBC; less effective than first-line agents [2] |
| Griseofulvin | 10 mg/kg daily (max 500 mg) | Prolonged courses required | Only 30-40% cure rate; high relapse; must be taken with fatty food [2] |
Family and Environmental Management
Screen all household members for onychomycosis and tinea pedis, as family transmission is common and all infected individuals should receive concurrent treatment. 2
Check the affected child for concomitant tinea capitis and tinea pedis. 2
Decontaminate or replace contaminated footwear and apply antifungal powders inside shoes regularly to prevent reinfection. 2
Avoid sharing nail clippers with infected family members. 2
Follow-Up and Monitoring
Monitor for at least 48 weeks from treatment initiation to detect potential relapse, as onychomycosis has high recurrence rates. 2
Re-evaluate clinical response at 3-6 months after starting therapy; consider additional treatment if disease persists. 2
Common Pitfalls to Avoid
Do not use topical agents alone for PSO in children—there are no pediatric clinical trials demonstrating efficacy, and systemic therapy is required for this deep infection pattern. 2
Do not use griseofulvin as first-line therapy—it achieves only 30% cure rates and requires prolonged treatment. 2
Do not skip mycological confirmation—the cost of diagnostic tests is always small relative to inappropriate and unnecessary long-term antifungal treatment. 1
Do not overlook immunosuppression screening in a child with PSO, as this presentation is uncommon in immunocompetent patients. 1, 4