What is the classification and treatment of cutaneous, subcutaneous, and deep fungal infections?

Classification and Treatment of Fungal Infections of the Skin and Soft Tissues

Fungal infections of the skin and soft tissues are classified into three main categories: cutaneous, subcutaneous, and deep infections, each requiring specific diagnostic and treatment approaches based on their invasiveness and causative organisms.

Classification of Fungal Infections

1. Cutaneous Fungal Infections

• Definition: Involve only the epidermis and dermis layers of skin
• Common examples:
  • Dermatophytoses (tinea infections)
  • Superficial candidiasis
  • Onychomycosis
• Causative organisms: Primarily dermatophytes capable of metabolizing keratin 1
• Clinical features: Erythematous, scaly patches, maceration, pruritus

2. Subcutaneous Fungal Infections

• Definition: Extend below the dermis into subcutaneous tissue but not into deeper structures
• Common examples:
  • Sporotrichosis (most common in North America)
  • Chromoblastomycosis
  • Mycetoma
  • Phaeohyphomycosis
• Causative organisms: Sporothrix schenckii, dematiaceous fungi, Pleosporales order fungi 1, 2
• Clinical features: Nodular lesions, ulcerations, draining sinuses, tissue deformity

3. Deep Fungal Infections

• Definition: Involve deep soft tissues, fascia, muscle, or bone
• Common examples:
  • Aspergillosis
  • Mucormycosis
  • Fusariosis
  • Invasive candidiasis
• Causative mechanisms:
  • Direct inoculation through trauma
  • Hematogenous dissemination from primary focus (often lungs) 3
• Clinical features: Necrotic ulcerations, eschar formation, rapidly progressive tissue destruction

Diagnostic Approach

For Cutaneous Infections:

• Direct microscopy with KOH preparation
• Fungal culture of skin scrapings or nail clippings
• Wood's lamp examination for certain infections

For Subcutaneous Infections:

• Tissue biopsy with histopathology is essential 3
• Fungal culture with species identification
• Molecular identification methods for difficult cases 2

For Deep Infections:

• Deep tissue biopsy (not surface swabs) is mandatory 3
• Histopathology with special stains
• Culture and molecular identification
• Blood cultures (though often negative in aspergillosis) 3

Treatment Approaches

1. Cutaneous Fungal Infections

• First-line: Topical antifungals (azoles, allylamines)
• For extensive or resistant cases: Oral antifungals
  • Terbinafine
  • Itraconazole
  • Fluconazole

2. Subcutaneous Fungal Infections

• Primary treatment: Systemic antifungal therapy 1
  • Itraconazole 200mg daily (treatment of choice for sporotrichosis) 2
  • Treatment duration: 2-10 months based on clinical response
• Adjunctive measures: Surgical debridement for localized lesions

3. Deep Fungal Infections

• Combined approach required:
  • Aggressive surgical debridement of necrotic tissue 1, 4
  • Systemic antifungal therapy

Specific Antifungal Regimens for Deep Infections:

• Aspergillosis:

  • Voriconazole (loading dose followed by maintenance) 5
  • Alternative: Liposomal amphotericin B

• Mucormycosis:

  • Amphotericin B (lipid formulation)
  • Surgical debridement is critical

• Fusariosis:

  • Voriconazole (high-dose) or posaconazole 3
  • Surgical intervention for localized disease

• Invasive Candidiasis:

  • Echinocandins (first-line)
  • Fluconazole for susceptible species

Special Considerations

Immunocompromised Patients

• Higher risk for invasive fungal infections
• Lower threshold for biopsy and aggressive treatment 3
• Broader empiric coverage may be necessary
• Longer duration of therapy typically required

Necrotizing Fungal Infections

• Require immediate surgical consultation 6
• Aggressive debridement is cornerstone of treatment
• Broad-spectrum antimicrobials including antifungals

Common Pitfalls to Avoid

1. Misdiagnosis: Mistaking fungal infections for bacterial cellulitis
2. Inadequate sampling: Surface swabs are inadequate; tissue biopsy is essential 3
3. Delayed surgical intervention: Particularly dangerous in necrotizing infections 6
4. Insufficient treatment duration: Subcutaneous and deep fungal infections require prolonged therapy
5. Overlooking underlying immunosuppression: Always consider host factors that predispose to fungal infections

By understanding the classification, diagnosis, and treatment approaches for different types of fungal infections, clinicians can provide timely and appropriate management to reduce morbidity and mortality associated with these conditions.