Which of the following is a bilateral differential diagnosis for epistaxis in horses?

• A. GP Mycosis
• B. Ethmoid Hematoma
• C. Sinusitis
• D. Neoplasia

Answer: (A)

When epistaxis is suspected to involve both nostrils, a differential that can affect both sides is considered. Guttural pouch mycosis can present with nosebleeds that arise from erosion of arterial walls by fungal invasion inside the guttural pouches, and while it often causes bleeding on one side, both pouches can be involved, leading to bilateral epistaxis. This makes guttural pouch mycosis a plausible bilateral cause to keep in mind.

Ethmoid hematoma typically presents as a mass within the ethmoid region and is usually unilateral, though rare bilateral cases can occur. Sinusitis can cause nasal discharge and discomfort and may bleed, but epistaxis is not a defining, bilateral feature. Neoplasia can involve either side and sometimes both, but the classic, notable source of bilateral nasal bleeding in horses from this list is guttural pouch disease due to its vascular involvement and potential to affect both sides.