Phaeohyphomycosis is a broad clinicopathologic designation that refers to chronic cutaneous, subcutaneous, or mucosal infection caused by one of several genera and species of pigmented fungi of the family Dematiaceae. Several fungal genera have been reported to affect humans and other animals including Alternaria, Bipolaris, Cladophialophora (Xylohypha, Cladosporium), Curvularia, Exophiala, Fonsecaea, Moniliella, Phialophora, Ramichloridium, and Scolecobasidium. Fungi in this category are saprophytic, widely distributed organisms found in soil, water, and decaying vegetable matter. Infection may result from fungal implantation into tissue at the site of an injury.

Clinical Findings and Lesions

Phaeohyphomycosis has been described in cows, cats, horses, and dogs. The most common clinical presentations include ulcerated cutaneous nodules, upper respiratory signs, and nasal/paranasal masses. Slowly enlarging, subcutaneous or submucosal masses are found about the head, nasal mucosa, limbs, and chest. The nodules may ulcerate and have draining fistulous tracts. These pyogranulomas contain pigmented, septate hyphae with irregular enlargements and thin-walled, budding yeast-like forms.

Diagnosis

Phaeohyphomycosis can be diagnosed by microscopic examination of exudate and biopsy specimens, which reveals pigmented or hyaline filamentous hyphae (2–6 μm in diameter), with terminal and intercalated vesicles (6–12 μm), and spores. The several causative fungi cannot be identified by their histologic features in tissues; cultural isolation and/or PCR are required. The differential diagnosis should include neoplasia, other granulomas, and epidermoid cysts.

Treatment

In most cases, the infection is confined to the skin and subcutaneous tissues. In a favorable location, cure can be effected by wide excision of the lesion. Chemotherapy with amphotericin B or itraconazole may be considered in cases when surgery is not possible.

Last full review/revision March 2012 by Joseph Taboada, DVM, DACVIM