To whom should a patient with toenail fungus, potentially with underlying health conditions such as diabetes or liver disease, be referred for proper evaluation and treatment?

When to Refer Patients with Toenail Fungus

Most patients with toenail onychomycosis can be managed in primary care with oral or topical antifungals, but referral to dermatology or podiatry is warranted for high-risk patients (diabetics, immunosuppressed individuals), diagnostic uncertainty, treatment failures, or when specialized nail procedures are needed. 1

High-Risk Patients Requiring Specialist Referral

Diabetic Patients

• Diabetic patients with onychomycosis should be referred to podiatry or dermatology because fungal nail infections can disrupt skin integrity, providing entry points for bacteria that lead to foot ulcers, osteomyelitis, cellulitis, and gangrene 1
• Up to one-third of diabetic patients have onychomycosis, with increased risk due to impaired glycemic control, ischemia, neuropathy, and local immunosuppression 1, 2
• The financial implications of neglecting onychomycosis in diabetics are substantial, making early specialist involvement cost-effective 1
• Diabetic neuropathy may mask progression of infection, and peripheral vascular disease increases risk of secondary complications 1, 2

Immunosuppressed Patients

• Refer HIV-positive patients, transplant recipients, and those on long-term corticosteroids or other immunosuppressive therapy 1, 3
• Approximately 30% of HIV-positive patients have onychomycosis, with prevalence correlating with CD4 counts 1
• Proximal subungual onychomycosis (PSO) without paronychia is uncommon and often indicates underlying immunosuppression or intercurrent disease requiring specialist evaluation 1
• Immunosuppressed patients have increased risk of atypical presentations and treatment-resistant infections 1, 3

Patients with Peripheral Vascular Disease

• Peripheral vascular disease increases risk of secondary bacterial infections and poor wound healing, necessitating specialist nail care 1
• These patients may develop cellulitis or more serious lower extremity complications from seemingly minor nail infections 1

Diagnostic Uncertainty Requiring Referral

When Clinical Diagnosis is Unclear

• Refer when nail dystrophy is present but fungal infection cannot be confirmed through microscopy and culture 1
• Approximately 50% of nail dystrophy cases are fungal in origin, but other conditions (psoriasis, trauma, lichen planus) can mimic onychomycosis 1
• Treatment should never be instituted on clinical grounds alone, as incorrect diagnosis is the most common cause of treatment failure in the UK 1

When Laboratory Testing is Negative but Clinical Suspicion Remains High

• Dermatology referral allows for nail biopsy to obtain full-thickness samples when surface scraping yields negative results 1, 4
• Specialists have access to more sophisticated diagnostic techniques including histopathology with periodic acid-Schiff staining 1

Treatment-Related Indications for Referral

Treatment Failures

• Refer after first-line terbinafine failure (evaluated 3-6 months post-treatment) for consideration of alternative systemic agents or combination therapy 5, 4
• Causes of treatment failure requiring specialist evaluation include poor absorption, subungual dermatophytoma, zero nail growth, or resistant organisms 4

Contraindications to Systemic Therapy

• Patients with active or chronic liver disease cannot receive terbinafine or itraconazole and require specialist management with topical therapy or alternative approaches 1, 5, 6
• Patients with lupus erythematosus have absolute contraindication to terbinafine 5
• Patients with significant drug interactions (multiple medications metabolized by CYP2D6) may benefit from specialist medication management 5

Need for Mechanical Intervention

• Refer when subungual dermatophytoma is present, as mechanical removal by trained professionals is necessary before antifungal therapy can be effective 1, 4
• Monthly professional nail debridement is integral to comprehensive onychomycosis management and should be performed by professionals trained in nail disorders 1, 7

Severe or Extensive Disease

Total Dystrophic Onychomycosis

• Total dystrophic onychomycosis (TDO) requires specialist management due to extensive nail plate involvement and need for prolonged, monitored therapy 1
• These cases may require up to 16 weeks of systemic therapy rather than standard 12-week courses 5

Multiple Nail Involvement

• Patients with involvement of multiple nails (especially all toenails or fingernails) benefit from specialist oversight for treatment optimization and monitoring 1

Special Populations

Pediatric Patients

• Children with suspected onychomycosis should be referred to pediatric dermatology as terbinafine is not FDA-approved for pediatric onychomycosis, though it may be used off-label 1, 5
• Pediatric dosing requires weight-based calculations: <20 kg receives 62.5 mg daily, 20-40 kg receives 125 mg daily, >40 kg receives 250 mg daily 5
• Onychomycosis in children represents only 1.5% of all nail dystrophies but is increasing in prevalence 1

Elderly Patients with Multiple Comorbidities

• Elderly patients on multiple medications may benefit from specialist review to minimize drug interactions and optimize treatment selection 5, 3
• Prevalence reaches 30% by age 60 and up to 50% in those over 70 years, often with concurrent conditions complicating management 1, 8, 3

When Primary Care Management is Appropriate

Primary care providers can manage uncomplicated dermatophyte toenail onychomycosis in healthy adults when:

• Diagnosis is confirmed by microscopy and culture 1
• No contraindications to systemic therapy exist 5
• Patient has no diabetes, immunosuppression, or peripheral vascular disease 1
• Baseline liver function tests and complete blood count are normal 5, 4
• Disease is limited to distal/lateral subungual pattern without total nail involvement 1

Treatment in primary care consists of terbinafine 250 mg daily for 12 weeks for toenails (6 weeks for fingernails) with re-evaluation at 3-6 months 5, 4