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Onychomycosis (Tinea Unguium)

BASICS

Description

  • Fungal infection of fingernails/toenails
  • Most common cause: dermatophytes (esp. Trichophyton rubrum), also yeasts (Candida) and nondermatophyte molds
  • Toenails affected > fingernails
  • Synonym: tinea unguium

EPIDEMIOLOGY

  • Worldwide prevalence: ~5.5%
  • Increases with age: 35% in adults >65 yrs; rare before puberty
  • Higher prevalence in immunocompromised (HIV: 15–40%), adults, those with comorbidities
  • Estimated: 50% of outpatient nail disorders

ETIOLOGY AND PATHOPHYSIOLOGY

  • Inoculation of nail by dermatophytes, nondermatophyte molds, or yeasts
  • Dermatophytes: Trichophyton (esp. T. rubrum), Epidermophyton, Microsporum
  • Yeasts: Candida albicans, C. parapsilosis, C. tropicalis, C. krusei
  • Molds: Scopulariopsis brevicaulis, Aspergillus sp., Alternaria sp.

RISK FACTORS

  • Older age, occlusive footwear, tinea pedis, cancer, diabetes, psoriasis
  • Peripheral vascular disease, smoking, immunodeficiency, living with others with onychomycosis
  • Use of communal pools, autosomal dominant genetic predisposition

GENERAL PREVENTION

  • Keep feet cool/dry; avoid occlusive shoes
  • Use sandals in public locker rooms/pools
  • Discard/treat infected footwear and socks

COMMONLY ASSOCIATED CONDITIONS

  • Immunodeficiency (HIV, transplant), diabetes
  • Tinea pedis/manuum

DIAGNOSIS

History

  • Nail discoloration, thickening, onycholysis

Physical Exam

  • Most often toenails (80%, esp. hallux)
  • Five clinical forms:
  • Distal/lateral subungual (most common): yellow-white/brown-black discoloration, subungual hyperkeratosis, onycholysis
  • Proximal subungual (rare): leukonychia beginning near cuticle, often with immunosuppression
  • Superficial onychomycosis: merging opaque white spots, may involve entire nail
  • Endonyx: milky nail with indentations, lamellar splitting, sparing nail bed

  • Total dystrophic: complete destruction of nail plate, thickened and ridged bed with debris

  • Candidal: mostly affects fingernails, often periungual tissue, white/yellow discoloration, mild pain

  • Mold: >60 yrs, more often hallux; resembles distal/lateral type

Pediatric Considerations

  • Superficial onychomycosis common in children with Candida
  • No FDA-approved systemic antifungals for children

Differential Diagnosis

  • Psoriasis, traumatic dystrophy, lichen planus, onychogryphosis, eczema, hypothyroidism, yellow nail syndrome, subungual melanoma, alopecia areata, chronic paronychia, pemphigus vulgaris

Diagnostic Tests

  • Direct microscopy (KOH prep) of nail sample
  • Culture (up to 30% false-negatives; slow)
  • Histology (PAS stain), PCR (rapid, sensitive), fluorescence microscopy
  • Discontinue topical antifungals 1 week before sampling
  • Confirm with laboratory evidence prior to treatment—50% of visual diagnoses are not fungal

TREATMENT

General Measures

  • Avoid moisture, treat risk factors (diabetes, immunodeficiency), treat secondary infections

First Line

  • Oral antifungals preferred for >50% nail involvement, multiple nails, nail matrix involvement, or dermatophytoma
  • Terbinafine: 250 mg/day PO × 6 weeks (fingernails) or 12 weeks (toenails); highest cure rates
  • Itraconazole pulse: 200 mg BID × 1 week/month × 2 cycles (fingernails), 3–4 cycles (toenails); no LFTs needed with pulse
  • Itraconazole continuous: 200 mg/day × 6 wks (fingernails), 12 wks (toenails)—less effective for dermatophytes, better for Candida/molds

Second Line

  • Fluconazole pulse: 150–300 mg PO weekly × 6 months (not FDA approved for onychomycosis)
  • Griseofulvin: up to 18 months, less effective, more side effects
  • Posaconazole, voriconazole: reserved for terbinafine-resistant
  • Topical agents (for <3 nails, distal disease only):
  • Efinaconazole 10% solution: once daily × 48 weeks
  • Ciclopirox 8% lacquer: daily × 48 weeks; >60% failure
  • Tavaborole 5% solution: daily × 48 weeks, cure rate ~15–18%

Contraindications for Oral Antifungals

  • Hepatic disease, pregnancy, CHF (itraconazole), porphyria (griseofulvin)

Precautions/Adverse Effects

  • Oral antifungals: hepatic/renal toxicity, numerous drug-drug interactions, CHF (itraconazole), photosensitivity (griseofulvin), hematologic effects
  • Topical: local rash, avoid on broken skin

Additional Therapies

  • Laser therapy (experimental)
  • Surgical or chemical nail avulsion, debridement
  • Photodynamic therapy (experimental)
  • Keratolytics (urea, salicylic acid, papain) pre-topical

Complementary & Alternative Medicine

  • Tea tree oil (no proven efficacy)
  • Vicks VapoRub (safe, unclear efficacy)

ONGOING CARE

  • New fingernail forms in 4–6 months, toenail in 12–18 months
  • Monitor topical therapy every 6–12 weeks
  • Monitor LFTs/CBC if on systemic therapy

PATIENT EDUCATION

  • Keep nails clean/dry, avoid occlusive footwear, change socks, avoid sharing nail tools
  • Cure may not be attainable; recurrences are common

PROGNOSIS

  • Complete cure: 25–50% with oral therapy
  • Recurrence: 10–50% within 5 years
  • Poor prognosis: >50% nail involvement, significant lateral/proximal disease, thick subungual hyperkeratosis (>2 mm), total dystrophic type, resistant organisms, immunosuppression, poor circulation

COMPLICATIONS

  • Secondary bacterial infections, cellulitis, osteomyelitis (esp. in diabetes)
  • Pain, mobility limitation, psychosocial impact

ICD-10 Codes

  • B35.1: Tinea unguium
  • B37.2: Candidiasis of skin and nail

Clinical Pearls

  • Psoriasis and trauma are common mimics.
  • Diagnosis requires clinical and laboratory confirmation.
  • Oral agents are more effective than topical, but recurrence is common.