Cleo, an 8-year-old spayed Swiss Mountain dog with unilateral nasal discharge (left > right), nasal stertor, difficulty breathing through the nose, and a firm mandibular lymph node. What are the top four differential diagnoses?

• A. Nasal neoplasia, aspergillosis, chronic rhinitis, tooth root abscess
• B. Nasal neoplasia, cryptococcus, aspergillosis, chronic rhinitis
• C. Nasal polyps, chronic rhinitis, nasal neoplasia, tooth root abscess
• D. Nasal neoplasia, cryptococcus, allergic rhinitis, tooth root abscess

Answer: (A)

When a dog presents with unilateral nasal discharge, nasal obstruction that causes stertor, and a firm mandibular lymph node, think about conditions that directly involve the nasal passages or sinuses and can provoke regional lymphatic spread. Nasal neoplasia is a leading concern because older dogs commonly develop tumors in the nasal cavity that produce unilateral discharge and obstruction, and regional lymph nodes can become enlarged as the disease progresses. Aspergillosis is another key possibility, especially in large-breed or dolichocephalic dogs; it typically causes a unilateral, foul or mucopurulent discharge with crusting and can destroy turbinate bone, leading to obstruction and facial pain, which fits the reported stertor and signs. Chronic rhinitis remains on the list because it can produce persistent nasal discharge and mucosal thickening, and although it often affects both sides, early disease or localized inflammation can be unilateral. A tooth root abscess is a plausible cause when the infection tracks from dental roots into the nasal cavity, causing unilateral discharge and frequently causing regional lymph node enlargement from chronic infection or inflammation.

Cryptococcus is a recognized nasal pathogen in dogs but is less common than these other causes in this species, and nasal polyps are far more typical in cats; allergic rhinitis usually presents with bilateral signs rather than a unilateral, localized process. In practice, imaging and sampling (cytology, biopsy, or culture) help distinguish these possibilities and guide targeted treatment, such as tumor management, antifungal therapy for fungal infections, dental treatment for abscesses, or anti-inflammatory/dental care for chronic rhinitis.