What are the characteristics of a fungal toenail infection?

Characteristics of Fungal Toenail Infection (Onychomycosis)

Fungal toenail infections typically present with nail discoloration, thickening, friability, and separation from the nail bed, often beginning at the distal or lateral edges and progressing proximally. 1

Clinical Patterns

Different clinical patterns of onychomycosis include:

1. Distal and Lateral Subungual Onychomycosis (DLSO)

   • Most common presentation (80-90% of cases)
   • Begins at distal/lateral nail edges and spreads proximally
   • Characterized by:
     • Thickened, discolored nail
     • Subungual hyperkeratosis (buildup under nail)
     • Onycholysis (separation of nail from nail bed)
     • Often associated with tinea pedis (athlete's foot) 1

2. Superficial White Onychomycosis (SWO)

   • Less common than DLSO
   • Affects the surface of the nail plate
   • Presents as:
     • White, crumbly patches on nail surface
     • Flaky appearance
     • Can spread to involve entire nail
     • More common in children
     • Usually caused by Trichophyton interdigitale 1

3. Proximal Subungual Onychomycosis (PSO)

   • Uncommon presentation
   • Infection begins at the proximal nail fold
   • Distal portion remains normal until late stages
   • Often associated with immunosuppression (e.g., HIV)
   • May indicate underlying conditions like diabetes or peripheral vascular disease 1

4. Total Dystrophic Onychomycosis (TDO)

   • Advanced stage of infection
   • Complete destruction of the nail plate
   • Entire nail becomes thickened, discolored, and crumbly 1

Causative Organisms

• Dermatophytes: Cause 90% of toenail and 75% of fingernail infections
  • Trichophyton rubrum (most common)
  • Trichophyton mentagrophytes 2, 3
• Yeasts: More common in fingernail infections
  • Candida species 4
• Non-dermatophyte molds: Emerging pathogens
  • Fusarium species most common 4

Clinical Features

Fungal nail infections typically present with:

• Nail discoloration (yellow, brown, white, or green)
• Thickening of the nail plate
• Brittle, friable nails that may break easily
• Onycholysis (separation of nail from nail bed)
• Subungual hyperkeratosis (debris under nail)
• Distorted nail shape
• Foul odor in some cases 2

Impact on Quality of Life

Onychomycosis is not merely a cosmetic concern but can significantly impact quality of life:

• Pain and discomfort (reported by approximately 50% of patients)
• Difficulty wearing footwear (30% of patients)
• Walking difficulties
• Emotional embarrassment and lowered self-esteem
• Work-related difficulties
• Risk of secondary bacterial infections
• Potential entry point for bacteria in diabetic patients, leading to complications 1

Diagnosis

Accurate diagnosis is essential before treatment:

• Clinical appearance alone is insufficient (approximately 50% of nail dystrophies are non-fungal)
• Laboratory confirmation recommended:
  • Direct microscopy with KOH preparation or calcofluor white staining
  • Fungal culture to identify specific pathogens
  • PAS staining of nail clippings (most sensitive method)
  • PCR assays for faster detection 5, 2

Differential Diagnosis

Non-fungal causes of nail dystrophy include:

• Psoriasis (pitting, onycholysis, oil-drop discoloration)
• Lichen planus (thinning, pterygium formation)
• Chronic trauma
• Bacterial infections (especially Pseudomonas causing green discoloration)
• Systemic conditions (e.g., iron deficiency anemia) 5

Prevention

Preventive measures to reduce risk of infection and recurrence:

• Avoid walking barefoot in public places
• Keep feet clean and dry
• Wear breathable footwear
• Disinfect shoes and socks
• Avoid sharing nail tools
• Allow time between artificial nail applications 5, 2

Fungal nail infections are chronic, difficult to treat, and have a high recurrence rate (approximately 25%), making proper identification and management essential for improving outcomes and quality of life 2.