Canine Nasal Disease Study Guide

Overview and Clinical Importance

Nasal disease represents a common yet diagnostically challenging condition in veterinary practice. The canine nasal cavity is a complex structure lined with highly vascular mucosa and delicate turbinate bones that serve crucial respiratory and olfactory functions. Chronic nasal discharge is one of the most frequent presenting complaints, with multiple etiologies including neoplasia, fungal infection (aspergillosis), foreign bodies, inflammatory rhinitis, and dental disease. Understanding the diagnostic approach and key differentiating features of each condition is essential for NAVLE success and clinical practice.

Nasal Anatomy Review

The canine nasal cavity extends from the external nares to the choanae (caudal openings into nasopharynx). The nasal septum divides it into two halves. Key anatomical structures include:

Nasal Turbinates (Conchae)

Dorsal nasal concha: Extends from ethmoid plate to nasal vestibule; longest turbinate

Ventral nasal concha: Attached to maxilla; largest surface area for air conditioning

Ethmoidal conchae: Fill caudal nasal cavity; 4 endoturbinates and 6 ectoturbinates in dogs; covered with olfactory epithelium

Nasal Meatuses

Four passages exist between turbinates: dorsal meatus (leads to olfactory region), middle meatus (communicates with paranasal sinuses), ventral meatus (main airway), and common meatus (alongside nasal septum).

Paranasal Sinuses

Dogs have three paranasal sinuses: frontal sinus (divided into rostral, medial, lateral compartments - most clinically significant), maxillary recess (not a true enclosed sinus), and sphenoidal sinus (small, filled by ethmoid turbinate). The frontal sinuses communicate with the nasal cavity via the nasofrontal opening.

Clinical Signs of Nasal Disease

The following clinical signs should prompt investigation for nasal disease:

Nasal Foreign Bodies

Nasal foreign bodies are a common cause of acute nasal disease in dogs. Over 90% of retrieved nasal foreign bodies are grass awns (including foxtails and cheatgrass). Other materials include plant matter, pebbles, sand, and toy fragments.

Signalment and Risk Factors

Studies show nasal foreign bodies are more common in: dogs less than 7 years old, dogs weighing greater than 10 kg (78.6% of cases), and male dogs (59.5%). Working dogs, hunting breeds, and highly active outdoor dogs are at increased risk due to exploratory sniffing behavior.

Clinical Presentation

• Acute onset paroxysmal sneezing (78.6% of cases) - often violent and persistent
• Pawing at nose or face rubbing
• Unilateral nasal discharge (initially serous, progressing to mucopurulent)
• Epistaxis if mucosal damage occurs
• History of outdoor activity, particularly in grassy areas

Diagnosis

Rhinoscopy is the diagnostic modality of choice for nasal foreign bodies and allows concurrent retrieval. CT scan is useful but detects only 42% of foreign bodies with confidence; a negative CT does not rule out foreign body. Foreign bodies typically appear linear (81%) with a "tubular-like appearance" (54%).

Chronic cases (greater than 7 days) show secondary changes on imaging: turbinate destruction and mucosal thickening are significantly associated with chronic foreign bodies.

Treatment

Prognosis: Excellent with prompt removal. Chronic cases may have persistent secondary bacterial rhinitis requiring extended antibiotic therapy.

Nasal Neoplasia

Nasal tumors account for 1-2% of all canine neoplasms but represent approximately 80% of chronic nasal disease cases in dogs. Nearly all nasal tumors in dogs are malignant.

Epidemiology and Tumor Types

Signalment: Mean age 9.5-10 years. Males affected more than females. Medium to large breed dogs at higher risk. Dolichocephalic and mesocephalic breeds predisposed (Collies, German Shepherds, Basset Hounds, Old English Sheepdogs). Ethmoturbinates are the most common site of origin.

Risk Factors

• Urban environment exposure to pollutants
• Environmental tobacco smoke
• Indoor fossil fuel combustion (kerosene, coal heaters)
• Previous flea spray exposure (some studies)

Clinical Signs

Chronic unilateral nasal discharge is the most common presenting complaint (often initially mucopurulent, progressing to hemorrhagic). As tumor advances:

• Discharge becomes bilateral
• Epistaxis develops (85% of dogs with nasal neoplasia)
• Facial deformity from bone destruction
• Exophthalmos with orbital invasion
• CNS signs (seizures, behavior changes, blindness) with cribriform plate invasion
• Epiphora if nasolacrimal duct blocked

Diagnosis

CT scan is the imaging modality of choice (92% accuracy vs 64% for rhinoscopy alone). CT findings include: soft tissue density mass, turbinate destruction, extension to frontal sinuses, and cribriform plate status.

Definitive diagnosis requires histopathology. Biopsy methods: rhinoscopy-guided, blind biopsy (do not advance forceps past medial canthus), CT-guided. Staging includes: mandibular lymph node assessment and 3-view thoracic radiographs.

Treatment and Prognosis

Sinonasal Aspergillosis

Sinonasal aspergillosis (SNA) accounts for 12-34% of chronic nasal disease in dogs. Caused primarily by Aspergillus fumigatus (most common), with A. flavus, A. niger, and A. nidulans less frequently implicated.

Pathophysiology

Aspergillus spores (conidia) are ubiquitous in the environment. SNA occurs in immunocompetent dogs - suspected local mucosal immune dysfunction allows colonization. Fungal invasion causes destructive rhinitis with turbinate necrosis (due to fungal endotoxins) and frontal sinus osteomyelitis. Severe cases can erode cribriform plate with CNS invasion.

Signalment

• Young to middle-aged dogs (mean 4.4 years) - substantially younger than neoplasia patients (mean 9.5 years)
• Dolichocephalic and mesocephalic breeds predisposed (Collies, Retrievers, Rottweilers, German Shepherds)
• Brachycephalic dogs rarely affected

Clinical Signs - The Three Hallmarks

• Profuse chronic nasal discharge - mucoid to hemorrhagic, often foul-smelling, alternating with epistaxis; typically UNILATERAL
• Nasal planum depigmentation and ulceration - CHARACTERISTIC finding for aspergillosis
• Facial pain/discomfort - dogs may resist palpation over nasal/frontal region

Diagnosis

Diagnosis requires 2 or more of the following criteria:

• CT/MRI findings: Turbinate destruction with hyperlucent nasal passages ("moth-eaten" appearance), frontal sinus involvement
• Rhinoscopy: Direct visualization of fungal plaques (white-grey-green colonies) - GOLD STANDARD for diagnosis
• Cytology/Histopathology: Septate, branching hyphae characteristic of Aspergillus spp. Best results from biopsy OF the plaque itself
• Serology/PCR: Positive antibody test or galactomannan antigen test. Note: serology has false positives (environmental exposure) and false negatives

Treatment

Topical antifungal therapy is the STANDARD OF CARE (systemic therapy has high failure rates and hepatotoxicity risk).

Prognosis: Good with topical therapy (86% success). Up to 25% may develop secondary bacterial rhinitis post-treatment requiring antibiotics. Nasal discharge typically resolves within 2 weeks of successful treatment.

Lymphoplasmacytic Rhinitis (LPR)

Idiopathic lymphoplasmacytic rhinitis (LPR) is the second most common cause of chronic nasal disease in dogs after neoplasia, accounting for approximately 30% of cases. It is a diagnosis of exclusion characterized by lymphoplasmacytic infiltration of the nasal mucosa without identifiable etiology.

Etiology and Pathophysiology

The etiology remains unknown. Proposed theories include: aberrant immune response to inhaled allergens or organisms, hypersensitivity to fungal organisms (including commensals), odontogenic infection, and gastrointestinal reflux. Dogs respond poorly to antibiotics, antihistamines, and glucocorticoids, making primary infectious, immune-mediated, or allergic etiologies unlikely as sole causes.

Signalment

• Median age 9 years (range 2-17 years)
• Large breed dogs most commonly affected
• No sex predilection
• Dachshunds may have breed predisposition

Clinical Signs

• Chronic nasal discharge (mucoid most common; may be unilateral or bilateral)
• Bilateral stertor (snoring breathing)
• Sneezing and reverse sneezing
• Epistaxis (less common than with neoplasia)
• Inspiratory dyspnea in severe cases

Diagnosis

LPR is a diagnosis of exclusion. All other causes of chronic nasal disease must be ruled out.

• CT/MRI: Often shows no overt changes or only mild turbinate opacification. Mild turbinate destruction possible but less extensive than neoplasia or aspergillosis.
• Rhinoscopy: Hyperemic, edematous, friable mucosa with mucus accumulation. No masses or fungal plaques.
• Histopathology (REQUIRED): Lymphoplasmacytic infiltration of nasal mucosa. MUST rule out lymphoma with immunohistochemistry (B- and T-cell markers) especially in severe cases.

Treatment

No consistently effective treatment exists. Most dogs have persistent clinical signs but can be managed long-term.

Prognosis: Guarded. Most dogs have chronic persistent signs. Quality of life can often be maintained with ongoing management. Rarely life-threatening but frustrating for owners.

Diagnostic Approach to Nasal Disease

Step-by-Step Algorithm

• History and Physical Examination: Duration, character of discharge (serous/mucopurulent/hemorrhagic), unilateral vs bilateral, sneezing pattern, facial deformity, nasal airflow assessment
• Rule out systemic causes of epistaxis: CBC (platelet count), coagulation panel (PT/PTT), blood pressure, tick-borne disease testing if indicated
• Advanced Imaging (CT preferred): Assess turbinate destruction, mass lesions, frontal sinus involvement, cribriform plate integrity
• Rhinoscopy: Visualize nasal cavity and nasopharynx, identify foreign bodies or fungal plaques, obtain biopsies
• Biopsy/Cytology/Culture: Histopathology is REQUIRED for definitive diagnosis of neoplasia and LPR. Fungal culture for aspergillosis.

Exam Focus: ALWAYS perform CT BEFORE rhinoscopy when neoplasia is suspected. Rhinoscopy causes hemorrhage and mucosal changes that can obscure CT findings. Exception: acute foreign body - rhinoscopy can be first-line for diagnosis AND treatment.

Key Differentiating Features

S = Stuck stuff (Foreign bodies)

N = Neoplasia

I = Inflammatory (LPR)

F = Fungal (Aspergillosis)

F = Fangs (Dental disease)