Exophiala

Background

• Genus of dematiaceous filamentous fungi
• Exophiala dermatitidis is the most clinically relevant "black yeast"

Clinical Manifestations

• Primarily in immunosuppressed or eldery patients
  • Most commonly, cutaneous and subcutaneous infection, including phaeohyphomycosis, chromoblastomycosis, keratitis, and nail infections
  • Also pneumonia, brain abscess, disseminated disease
• Exophiala dermatitidis is neurotropic, with high mortality, and this can occur in immunocompetent (often Asian) patients
• Known to colonize cystic fibrosis patients (3-20%)

Diagnosis

• On histology of cutaneous infection, shows epidermal hyperkeratosis, hyperplasia, acanthosis, pseudoepitheliomatous and intraepidermal pustules
• Culture
  • Colony: yeast-like, black, and mucoid
  • Microscopy
    • Can have pigmented fungal elements within or adjoining multinucleate giant cells
    • Yeast form is budding and black, while filamentous form is septate and pigmented.

Management

• No validated clinical breakpoints to guide therapy
• Itraconazole or oral terbinafine, alone or in combination
• Amphotericin B is also commonly used, and voriconazole also likely works
• Echinocandins are likely ineffective