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

• A. Trauma
• B. GP Mycosis
• C. EIPH
• D. Coagulopathy

Answer: (A)

Epistaxis that affects only one nostril points to a local lesion on that side rather than a systemic or bilateral process. A direct injury to the nasal mucosa or surrounding structures—trauma to the face or nose—can rupture a vessel unilaterally, producing bleeding from a single side. This makes trauma a straightforward unilateral differential in horses presenting with one-sided nasal bleeding.

It's helpful to contrast the other options: exercise-induced pulmonary hemorrhage comes from the lungs and typically results in blood seen from both nostrils after strenuous exercise, not confined to one side. A coagulopathy reflects a systemic bleeding tendency and often leads to bilateral or widespread bleeding rather than a localized unilateral epistaxis. Guttural pouch mycosis is indeed a well-known unilateral cause because it can erode a vessel on one side of the guttural pouch, but in the context of a general unilateral differential for epistaxis, a simple traumatic injury to the nasal region is the most direct and common unilateral explanation.