Feline Chronic Sinusitis Study Guide

Overview and Clinical Importance

Feline chronic rhinosinusitis (FCRS) is defined as inflammation of the nasal cavity and paranasal sinuses persisting for more than four weeks or recurring intermittently. This condition represents the second most common cause of feline nasal disease after neoplasia, accounting for approximately 35-55% of cases in referral settings. The disease is characterized by chronic, typically bilateral mucopurulent nasal discharge, sneezing, and stertorous breathing.

The pathogenesis involves initial viral damage, most commonly from feline herpesvirus-1 (FHV-1) or feline calicivirus (FCV), which leads to turbinate destruction and mucosal damage. This creates a self-perpetuating cycle of secondary bacterial infection, chronic inflammation, and further structural damage. Approximately 80% of cats experience neuronal latency of FHV-1 in the trigeminal ganglion, allowing viral reactivation during stress or immunosuppression.

Etiology and Pathophysiology

Primary Viral Etiology

Feline Herpesvirus-1 (FHV-1) is considered the common denominator initiating turbinate resorption. The virus causes epithelial necrosis and osteolysis of nasal turbinates through direct cytolytic effects. Following acute infection, FHV-1 establishes latency in the trigeminal ganglion, where it can reactivate during periods of stress, illness, or immunosuppression.

Feline Calicivirus (FCV) may also contribute to initial mucosal damage. Unlike FHV-1, FCV infection results in a carrier state with continuous viral shedding for variable periods rather than true latency.

Pathophysiologic Cascade

Clinical Signs and Presentation

Classic Presentation

FCRS can occur in cats of any age, though young-to-middle-aged cats are commonly affected. Clinical signs often last more than 4 weeks and include:

Physical Examination Findings

General examination is often unremarkable aside from nasal findings. Perform systematic assessment:

• Nasal airflow assessment: Use a cold glass slide, mirror, or cotton wisps to assess patency of both nasal passages
• Facial symmetry: Facial deformity or complete airflow obstruction suggests alternative diagnosis (neoplasia, cryptococcosis)
• Dental examination: Assess for periodontal disease, tooth root abscess, oronasal fistula
• Frontal sinus auscultation: May be revealing using a small pediatric stethoscope bell
• Lymph node palpation: Mandibular lymphadenopathy may indicate inflammation or neoplasia

Differential Diagnosis

FCRS is a diagnosis of exclusion. Alternative causes of chronic nasal signs must be ruled out before establishing this diagnosis.

Diagnostic Approach

Initial Database

The minimum database for chronic nasal disease includes:

Advanced Imaging

Computed Tomography (CT) is the preferred imaging modality for chronic nasal disease, providing superior visualization of turbinate structures, sinuses, and bone compared to radiography.

Rhinoscopy and Biopsy

Rhinoscopy should be performed AFTER imaging to avoid blood/fluid artifact. Use a rigid 1.9mm arthroscope with 30-degree viewing angle for rostral nasal cavity, or retroflex flexible endoscope for caudal nasopharynx.

Rhinoscopic findings in FCRS:

• Normal turbinate mucosa: pale pink, smooth
• FCRS: Hyperemia, irregular turbinate surfaces, moderate mucus exudation
• Even if mucosa appears normal, ALWAYS biopsy in chronic disease
• Histopathology typically shows lymphoplasmacytic or neutrophilic inflammation

Treatment and Management

Treatment goals: Reduce clinical signs, control secondary infection, improve quality of life. FCRS is NOT curable - clients must understand the need for long-term management.

Antibiotic Therapy

Duration: Continue antibiotics for 6-8 weeks minimum without changing if initial positive response. Choose antibiotics that penetrate bone and cartilage due to chronic osteomyelitis.

Antiviral Therapy

Consider if FHV-1 reactivation suspected (stress-related flares, concurrent ocular signs):

Anti-inflammatory and Supportive Therapy

Surgical Intervention

Surgery is reserved for cases refractory to medical management:

• Frontal sinus trephination: Drilling openings into frontal sinus for drainage, flushing, and sample collection
• Frontal sinus ablation: Removal of mucoperiosteal lining, necrotic turbinates, obliteration with autogenous fat graft
• Rhinotomy with turbinectomy: For removal of severely necrotic tissue. May result in persistent loss of smell.

Prognosis and Client Communication

Prognosis is guarded for resolution of clinical signs. Key points for client communication:

• FCRS is a chronic, incurable condition requiring lifelong management
• Clinical signs (sneezing, discharge) may never completely resolve
• Periodic flares are expected, especially during stress
• Goal is to improve quality of life, not cure
• Cats with marked turbinate destruction have poorer response to treatment
• Younger cats (less than 2 years at onset) may have more severe disease