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Tuesday, August 12, 2025

Fungal nail infection


Definition

Fungal nail infection, also called onychomycosis, is a common nail disorder caused by the invasion of fungi into the nail plate, nail bed, or both. It leads to nail discoloration, thickening, deformity, and potential pain or discomfort.

Epidemiology

  • Affects around 10% of the general population, rising to >20% in those over 60 years

  • More common in men than women

  • Higher prevalence in individuals with chronic conditions such as diabetes, peripheral vascular disease, and immunosuppression

Causes and Pathogens

Main causative organisms:

  • Dermatophytes (most common)

    • Trichophyton rubrum (predominant)

    • Trichophyton interdigitale

  • Non-dermatophyte moulds

    • Scopulariopsis brevicaulis

    • Fusarium spp.

  • Yeasts

    • Candida albicans (more common in fingernails, especially in chronic paronychia)

Risk Factors

  • Increasing age

  • Nail trauma or repetitive microtrauma

  • Occlusive footwear

  • Excessive sweating (hyperhidrosis)

  • Swimming pool or communal shower use

  • Poor peripheral circulation

  • Immunosuppression (HIV, post-transplant, long-term corticosteroid use)

  • Diabetes mellitus

  • Psoriasis

  • Previous tinea pedis (athlete’s foot)

Pathophysiology

Fungal spores invade the keratinized tissues of the nail plate or bed, producing enzymes (keratinases, proteases) that degrade keratin. This leads to progressive nail destruction, thickening, and discoloration.

Clinical Types of Onychomycosis

  1. Distal lateral subungual onychomycosis (DLSO) – most common

    • Begins at distal/lateral nail edges; spreads proximally

  2. White superficial onychomycosis (WSO)

    • Chalky white patches on nail surface

  3. Proximal subungual onychomycosis (PSO)

    • Starts near the cuticle; often seen in immunocompromised

  4. Total dystrophic onychomycosis (TDO)

    • End stage with complete nail destruction

Symptoms and Signs

  • Nail discoloration: yellow, brown, white, or black

  • Thickened nails (onychauxis)

  • Nail plate distortion and crumbling

  • Subungual hyperkeratosis

  • Brittleness and rough surface

  • Possible mild pain or discomfort in severe cases

Diagnosis

Clinical suspicion is supported by:

  • Appearance of nail changes

  • History of risk factors

Laboratory confirmation (recommended before systemic therapy):

  • Microscopy: Potassium hydroxide (KOH) preparation to detect fungal hyphae

  • Culture: Identifies species and guides treatment

  • Histopathology: Periodic acid–Schiff (PAS) staining of nail clippings

Differential Diagnosis

  • Psoriasis

  • Lichen planus

  • Trauma-induced nail dystrophy

  • Eczema involving the nails

  • Yellow nail syndrome

Management

Treatment depends on severity, number of nails involved, and patient comorbidities.

1. General Measures

  • Keep nails short and clean

  • Wear breathable footwear and cotton socks

  • Treat coexisting tinea pedis to prevent reinfection

  • Disinfect shoes and nail instruments regularly

2. Topical Antifungals

Best for mild disease (<50% of nail surface, no matrix involvement, ≤3 nails affected):

  • Amorolfine 5% nail lacquer

    • Apply once or twice weekly to affected nails after filing surface

    • Duration: 6 months (fingernails) to 9–12 months (toenails)

  • Ciclopirox 8% nail lacquer

    • Apply daily to affected nails, remove with alcohol every 7 days

    • Duration: 6–12 months

3. Systemic Antifungals

Indicated for extensive disease, involvement of nail matrix, or failure of topical therapy. Confirm diagnosis before starting systemic treatment.

  • Terbinafine (first-line for dermatophytes)

    • 250 mg orally once daily for 6 weeks (fingernails) or 12 weeks (toenails)

    • Monitor liver function before and during therapy

  • Itraconazole (alternative; covers dermatophytes, yeasts, some moulds)

    • Continuous: 200 mg orally once daily for 6 weeks (fingernails) or 12 weeks (toenails)

    • Pulse: 200 mg orally twice daily for 1 week per month; 2 pulses (fingernails) or 3–4 pulses (toenails)

  • Fluconazole (off-label; mainly for Candida)

    • 150–300 mg orally once weekly until nail regrowth (6–12 months)

4. Combination Therapy

Topical + systemic antifungal therapy can improve cure rates, especially in severe or resistant cases.

5. Surgical or Chemical Nail Avulsion

  • Consider for severely damaged nails or when antifungal therapy is contraindicated

  • Chemical avulsion: 40% urea paste applied under occlusion

Follow-up and Prognosis

  • Nails grow slowly: complete regrowth takes ~6 months for fingernails, 12–18 months for toenails

  • Relapse/reinfection rate: 20–25% within 2 years

  • Good adherence to therapy and preventive measures improves outcome




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