Onychomycosis

Fungal infection of the nails (fingernails or toenails), most commonly caused by dermatophytes, but can also involve yeasts (Candida) or non-dermatophyte molds

Aetiology

1. Dermatophytes (most common)
  • Trichophyton rubrum (majority of cases)
  • Trichophyton mentagrophytes
2. Yeasts
  • Candida albicans (more common in fingernails)
3. Non-Dermatophyte Molds
  • Scopulariopsis, Fusarium, Aspergillus

Predisposing Factors

  • Age > 60 years
  • Diabetes mellitus
  • Peripheral vascular disease
  • Immunosuppression (HIV, corticosteroids)
  • Trauma or repeated microtrauma
  • Tinea pedis
  • Occlusive footwear
  • Hyperhidrosis

Pathophysiology

  1. Malassezia exists normally as yeast on the skin.
  1. Predisposing factors trigger conversion to the pathogenic mycelial form.
  1. The fungus produces azelaic acid and other metabolites.
  1. These substances inhibit tyrosinase activity in melanocytes.
  1. This leads to hypopigmented or hyperpigmented macules with fine scaling.

Clinical Presentation

  • Distal Lateral Subungual Onychomycosis (DLSO)
    • Most common type
    • Starts at distal/lateral nail edge → proximal spread
    • Nail thickening, crumbly texture, yellow-white discoloration
  • White Superficial Onychomycosis (WSO)
    • White chalky patches on nail surface
    • Easy scraping
  • Proximal Subungual Onychomycosis
    • Affects proximal nail fold
    • Seen more in immunocompromised individuals (HIV)
  • Endonyx Onychomycosis
    • Nail plate invasion without subungual hyperkeratosis
    • Diffuse milky discoloration
  • Total Dystrophic Onychomycosis
    • Advanced disease with complete nail destruction

Clinical Features

  • Nail discoloration (dyschromia): yellow, brown, white
  • Nail thickening & subungual hyperkeratosis
  • Brittleness, crumbling, onycholysis (nail lifting from bed)
  • Dull opaque appearance
  • May be asymptomatic initially
  • Pain & difficulty walking in severe cases (toenails)
notion image

Investigations

  • KOH 20% Examination
    • Shows true/long hyphae with arthrospora (tinea unguium) or yeast cells (pseudohyphae with blastospora)

Management

  • 1st line
    • Finger Nail → Terbinafine 250 mg 1x1 for 6 weeks
    • Foot Nail → Terbinafine 250 mg 1x1 for 12-16 weeks
  • 2nd line
      • Itraconazole pulse dose ( 1 week therapy, 3 weeks off)
    • Finger Nail → 200 mg 2x1 (2 pulse doses)
    • Foot Nail → 200 mg 2x1 (3-4 pulse doses)