For yellow-white purulent nasal discharge, which is among the top differential diagnoses?

• A. GP Mycosis
• B. Strangles
• C. Cicatrix
• D. Pneumonia

Answer: (A)

The main idea is that persistent purulent nasal discharge in a horse, especially when it is yellowish to creamy and unilateral, most strongly points to guttural pouch disease. Guttural pouch mycosis is a fungal infection inside the guttural pouch that commonly drains through the nasal cavity as a yellow‑white, purulent discharge. It’s a top consideration because the pouch sits right behind the nasal passages, so infection there directly vents into the nostril and can persist despite simple nasal treatments.

This condition often brings clues beyond just discharge: it can erode nearby vessels and nerves, leading to nosebleeds or cranial nerve deficits, which helps distinguish it from other causes. In contrast, Strangles can also cause purulent nasal discharge but is typically accompanied by fever and swollen lymph nodes, and the discharge pattern is less characteristically unilateral and persistent. Cicatrix is scar tissue and doesn’t cause ongoing purulent discharge, and pneumonia is a lung disease with nasal discharge as a less central feature and more systemic signs.

So, for yellow-white purulent nasal discharge in a horse, guttural pouch mycosis stands out as a top differential because of its location, typical discharge pattern, and potential for associated cranial nerve signs or epistaxis. Diagnosis is via endoscopy and imaging of the guttural pouches, with treatment focused on antifungal therapy and management of any complications.