THE MERCK VETERINARY MANUAL
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Rhinitis and Sinusitis in Small Animals

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Inflammation of the mucous membranes of the nose and sinuses may be acute or chronic.

Viral infection is the most common cause of acute rhinitis or sinusitis in dogs and cats. Feline viral rhinotracheitis (FVR), feline calicivirus (FCV), canine distemper, canine adenovirus types 1 and 2, and canine parainfluenza are most frequently incriminated. Chronic states exist for FVR and FCV, with intermittent shedding associated with stress. Bacterial rhinitis or sinusitis frequently is a secondary complication. Primary bacterial rhinitis is extremely rare in dogs. It may result from infection with Bordetella bronchiseptica in dogs. Bacterial rhinitis appears to be a common complicating factor in cats with chronic rhinosinusitis, although exposure to environmental aeroallergens may also play a role. Allergic rhinitis or sinusitis is a poorly defined atopy that may occur seasonally, possibly in association with pollen production, or perennially, probably in association with house dusts and molds. Smoke aspiration, inhalation of irritant gases and dusts, or foreign bodies lodged in the nasal passages also may cause acute rhinitis.

Chronic rhinitis is commonly complicated by secondary bacterial colonization or infection because the primary nasal disease results in increased mucus production and altered mucociliary clearance of debris within the nose. Underlying causes of chronic rhinitis include idiopathic chronic inflammatory disease (lymphoplasmacytic rhinitis), trauma, parasites (Cuterebra), foreign bodies, neoplasia, or mycotic infection. In cats, chronic rhinosinusitis is a frequent sequela of acute viral infections of the nasal and sinus mucosa that result in hyperplastic glandular and epithelial changes. Rhinitis or sinusitis may result when an apical tooth root abscess extends into the maxillary recess. Mycotic rhinosinusitis may be caused by Cryptococcus neoformans, Aspergillus spp, and Penicillium spp. Cats are more often affected with Cryptococcus spp than dogs, whereas aspergillosis is frequent in dogs but rare in cats.

Acute rhinitis is characterized by nasal discharge, sneezing, pawing at the face, respiratory stertor, open-mouth breathing, and/or inspiratory dyspnea. Lacrimation and conjunctivitis often accompany inflammation of the upper respiratory passages. Affected tissues are often hyperemic and edematous. The nasal discharge is serous but becomes mucoid as a result of secondary bacterial infection. If inflammatory cells infiltrate the mucosa, the discharge may become mucopurulent. Sneezing, in an attempt to clear the upper airways of discharge or exudate, is seen most frequently in acute rhinitis and tends to be intermittent in chronic rhinitis. Aspiration reflex (“reverse sneeze”), a short paroxysmal episode of inspiratory effort in an attempt to clear the nasopharynx of obstructing material, may also be seen.

Respiratory stertor, open-mouth breathing, and inspiratory dyspnea occur when the nasal passages are narrowed from inflamed mucosa, glandular elements, and secretions. An acute unilateral nasal discharge, possibly accompanied by pawing at the face, suggests a foreign body. Neoplastic or mycotic disease is suggested by a chronic nasal discharge that was initially unilateral but becomes bilateral or that changes in character from mucopurulent to serosanguineous or hemorrhagic. Approximately 35% of cats with nasal cryptococcosis have facial deformity (dorsal lump) of the rostral aspect of the nose. Head shyness or facial pain is more commonly associated with fungal rhinitis in dogs.

Diagnosis is based on history, physical examination, radiographic findings (especially CT), rhinoscopy, nasal biopsy, deep nasal tissue culture, and elimination of other causes of nasal discharge and sneezing. Advanced imaging studies and biopsy may identify a specific etiologic diagnosis for nasal discharge (eg, fungal rhinitis, neoplasia, foreign body) in as few as 36% of cats and 63% of dogs with chronic nasal disease.

Serum titer for cryptococcal antigen is a very specific and sensitive test for nasal cryptococcosis. Serologic evaluation for aspergillosis is more problematic in that negative test results do not exclude infection. Nasal tissue culture for Aspergillus may also result in false-positive results; as many as 30% of normal dogs and 40% of dogs with nasal neoplasia have positive culture results. The combination of seropositivity for and culture identification of Aspergillus is highly suggestive of infection, although negative test results do not exclude nasal aspergillosis. Direct sampling of visualized suspected fungal plaques may potentially yield Aspergillus hyphae in all cases.

In mild or acute cases, supportive treatment may be effective. Severe cases of rhinosinusitis in kittens or adult cats may require parenteral fluids to prevent dehydration, and nutritional support via a nasogastric tube to maintain weight. Chronic secondary bacterial rhinosinusitis may be treated with antimicrobial chemotherapy for 3–6 wk. Intermittent use of vasoconstrictive nasal decongestants usually provides only temporary relief of congestion.

Mycotic rhinosinusitis requires antifungal therapy based on identification of a fungal etiologic agent. Fluconazole (50–100 mg/day, PO) or itraconazole (50–100 mg/day, PO) may be effective for treatment of nasal cryptococcosis in cats. Oral antifungal agents have variable efficacy in treatment of dogs with nasal aspergillosis, although voriconazole (4 mg/kg, PO, bid) alone or in combination with terbinafine (15 mg/kg, PO, bid for 1 mo) may be effective. Topical intranasal infusions of enilconazole or clotrimazole or combined clotrimazole solution and cream depot therapy instilled via the frontal sinuses have success rates as high as 50% for the first treatment and 90% with two treatments, although reinfection or relapse may occur.

Animals that do not respond to medical therapy may require surgery consisting of sinusotomy or rhinotomy, lavage, and biopsy to reestablish definitive diagnosis. Radiation therapy is the most viable treatment for intranasal neoplasia.

Last full review/revision November 2013 by Ned F. Kuehn, DVM, MS, DACVIM

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