Hyalohyphomycosis is infection caused by nonpigmented fungi (other than the genera Aspergillus or Penicillium or the class Zygomycetes) that in tissue form hyphal elements with hyaline or clear walls. Examples of genera causing hyalohyphomycosis in people and other animals include Acremonium, Fusarium, Geotrichum, Paecilomyces, Pseudallescheria, Sagenomella, Phialosimplex, Geosmithia, Geomyces, and Scedosporium. Hyalohyphomycosis is far less common than phaeohyphomycosis.
Lesions range from local cutaneous, subcutaneous, corneal, or nasal mucosal disease to disseminated disease involving the lungs and multiple other organ systems. Disseminated and corneal forms have been reported most commonly. Animals presenting with cutaneous lesions should be evaluated for systemic disease. Animals being treated with immunosuppressive drugs for immune-mediated disease may develop cutaneous hyalohyphomycosis and not have lesions at other sites, whereas immunocompetent animals that develop hyalohyphomycosis most often do have disseminated disease, or at least disease that is not confined to the skin.
The several causative fungi cannot be identified by their histologic features in tissues; culture isolation and/or PCR are required.
Surgical removal with or without azole antifungal therapy is the treatment of choice for local disease. Disseminated disease typically carries a grave prognosis. Treatment with newer azole antifungals and/or amphotericin B lipid complex may be attempted and is most likely to be effective if immunosuppressive drugs can be tapered.