Phaeohyphomycosis

Phaeohyphomycosis

Phaeohyphomycosis is a general term used to describe infections caused by dematiaceous (dark-pigmented) fungi. These fungi are widespread saprophytes and the disease occurs worldwide.

It is a rare disease of horses and several dematiaceous species have been implicated, including Alternaria alternaria, Pseudallescheria boydii, Bipolaris spicifera and Curvularia geniculata.

The fungi enter via a wound or at the site of trauma and produce a granulomatous nodule or mass involving the dermis at or near the site of entry. Location is variable and can be nasal, paranasal, chest, head and limbs. The nodules enlarge, ulcerate and have fistulous tracts. It may spread peripherally and, on occasion, to the lymphatics and other tissues and organs. The disease is chronic and if not treated it may persist and progress.

Diagnosis

Laboratory examination is necessary to distinguish this disease from others with somewhat similar features.

• Material from granulomatous lesions and biopsies or portions of lesions, fixed: The characteristic brown/dark-pigmented, branching, hyphal elements can be seen in wet mounts. The same fungal structures are seen in stained sections. Finding the fungal elements in tissue sections is confirmatory.
• Definitive diagnosis is based on the isolation and identification of the fungus, which may take as long as 6 weeks to grow. The precise identification of the fungus may have to be carried out in a reference laboratory.

Treatment

• Surgical excision of the lesion in some cases. Amphotericin B, locally and systemically. The imidazole drugs may be effective.