Phaeohyphomycotic Rhinitis Caused by Bipolaris hawaiiensis in a Horse

This case represents the first reported case of Bipolaris hawaiiensis infection in an equid, and its aggressive clinical course. This case provides important descriptive and prognostic information for horses diagnosed with phaeohyphomycotic rhinitis. A 19-year-old American Quarter Horse mare was presented for second opinion of stertor and exercise intolerance of four-month duration. Endoscopy revealed generalized, proximal nasal edema, and computed tomography identified a soft tissue mass eroded through the rostral nasal bone. Biopsy of the mass was identified as a fungal granuloma caused by B. hawaiiensis resulting in chronic invasive fungal rhinitis. Treatment options were limited because of invasive infection, financial constraints, fungal sensitivity results, and published accounts of in vivo behavior of the organism. The infection progressed, resulting in euthanasia. In this case of equine phaeohyphomycosis, B. hawaiiensis was likely traumatically introduced into the patient's nasal cavity. Its aggressive nature in an apparently immunocompetent patient is noteworthy, in the face of surgical debridement and attempted medical therapy. Therapeutic decisions were challenging in this case based on limited in vivo efficacy data in equids, pharmacokinetic challenges with available antifungal agents, and client-driven limitations regarding management of airway restriction.