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Chronic Rhinosinusitis in Cats

Leah A. Cohn, DVM, PhD, Diplomate ACVIM (Small Animal Internal Medicine), and Eric Pope, DVM, MS, Diplomate ACVS, Ross University

Respiratory Medicine

November 2007
Peer Reviewed

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  • CRS is a syndrome characterized by inflammation of the nasal passages and sinuses that results in persistent or recurrent nasal discharge and sneezing and that defies specific etiologic diagnosis.
  • Although CRS is encountered with some frequency, estimates of incidence and prevalence are lacking.


  • Cats of any breed or age and either gender may be affected.
  • By definition, the cause of CRS is undetermined. Efforts must be made to rule out specific causes of nasal discharge and associated clinical signs.
  • Cats with previous respiratory viral infection may be at greater risk.
  • The pathophysiology of CRS is not understood. Previous viral respiratory infection may predispose to CRS.
    • FHV-1 (also called rhinotracheitis) and FCV are common causes of acute upper respiratory tract infection in kittens and naïve cats. Although acute infection is typically self-limiting, FHV-1 is not cleared; instead, cats become latent carriers. Similarly, cats may remain carriers of FCV for years.
  • Latent infection might become "reactivated," especially during stress. A role for active viral infection in naturally occurring rhinosinusitis has not been documented.
  • Viral infection may lead to cytolysis and subsequent damage to physical nasal defense mechanisms. This would, in turn, predispose to repeated secondary bacterial infection.
  • Viral infection may initiate or perpetuate inflammation, leading to an "immune-mediated" inflammatory process within the upper respiratory epithelial tissues.
    • The nasal passages and sinuses are not normally sterile but contain a wide variety of microbes, including Streptococcus species, Staphylococcus species, Corynebacterium species, Pasteurella multocida, Escherichia coli, Klebsiella species, Enterobacter species, and Pseudomonas aeruginosa. Bacterial infection in CRS is probably a secondary rather than primary phenomenon.
    • Both lymphoplasmacytic and neutrophilic inflammation have been reported in nasal specimens from cats with CRS.


  • History consists primarily of chronic persistent or recurrent episodes of nasal discharge. Discharge can be unilateral but is more commonly bilateral, and is often mucopurulent in character. Sometimes, discharge may be blood tinged.
  • Other common historical clinical signs include sneezing, stertorous breathing, and ocular discharge.
  • Less commonly, vomiting, coughing, and anorexia are reported.
  • Physical examination is generally unremarkable save for findings related to nasal passages and sinuses. Nasal discharge may be visible, but the fastidious nature of cats may result in grooming and rapid removal of discharge.
  • Facial deformity, complete obstruction of airflow, and severe dental disease suggest alternative diagnosis.

Pain Index

  • Although probably not painful, CRS may cause discomfort.


Definitive Diagnosis

  • There is no definitive diagnosis of CRS. Instead, alternative definitive causes of chronic nasal signs should be ruled out.

Differential Diagnosis

  • Differential diagnosis for cats with an acute onset and short duration of nasal signs differs from that for cats with chronic, persistent, or recurrent nasal signs.
  • Differential diagnoses for cats with chronic signs include nasal neoplasia (most commonly lymphoma and carcinoma), fungal rhinitis (usually cryptococcosis), periodontal disease, nasopharyngeal polyps, and nasal foreign bodies.
  • Differential diagnoses for acute presentations include all those mentioned for cats with chronic nasal signs, plus viral (FHV-1 and FCV) and bacterial (Chlamydophila felis, Bordetella bronchiseptica) infections.

Laboratory Findings/Imaging

  • Routine tests such as CBC, serum chemistry profile, urinalysis, and retroviral serology are useful to determine overall health status but do not contribute to the diagnosis of this clinical syndrome.
  • Radiographs or CT scans may be unremarkable or may demonstrate increased fluid opacity in the nasal passages and sinuses. Sometimes loss of the normal turbinate pattern may be seen.
  • Bacterial cultures may reflect the presence of colonizing bacteria and do not prove a causative role for microbial infection. Culture of nasal discharge is not warranted. Culture of nasal biopsy tissue may provide some useful information but is not uniformly required.
  • Viral isolation, viral serology, and polymerase chain reaction assays for FHV-1 and FCV are generally not indicated.
  • Rhinoscopy may be unremarkable or may demonstrate mucus or hyperemia in affected nasal passages.
  • Destruction or distortion of turbinates is sometimes visualized during rhinoscopy.
  • Nasal biopsy may demonstrate neutrophilic or lymphoplasmacytic inflammation. It is most useful to rule out differential diagnoses including nasal neoplasia.


Medical Treatment
Differential diagnoses must be ruled out before empiric treatment of CRS.

  • Although bacterial infection probably plays a secondary rather than a primary role in CRS, antimicrobial therapy is beneficial in the treatment of many cats.
  • Frequent changes in antimicrobial therapy may promote infection with antimicrobial-resistant bacterial species.
  • Antimicrobial therapy can be directed toward specific respiratory pathogens or can be administered palliatively.
    • Specific therapy is directed by results of culture and sensitivity or aimed at pathogens with potential importance, including B bronchiseptica and Mycoplasma species. Tetracycline derivatives or fluoroquinolones are often effective for the treatment of these organisms. A 3-week course of treatment should be sufficient to treat these infections.
    • Palliative therapy uses antimicrobials with a broad therapeutic index over a long period (6 to 8 weeks). Amoxicillin or clavulanic acid-amoxicillin combinations are frequently used for this purpose. If the cat does not improve within a week, further treatment is not warranted. There is no evidence that azithromycin is preferred over amoxicillin for palliative therapy. Courses of palliative antibiotic therapy can be repeated. The antimicrobial chosen should not be altered if still effective clinically.
  • Additional therapies for CRS have been used but have not been scientifically evaluated. These therapies include both physical and drug therapies.
    • Nasal lavage accomplished under general anesthesia sometimes helps temporarily relieve clinical signs and may dislodge hidden nasal foreign material.
    • Humidification is helpful. This can be accomplished with room humidifiers or by placing the cat in a bathroom with a hot shower running. Instillation of nasal saline drops can also be useful, as can saline nebulization.
    • L-lysine is used to inhibit FHV-1 replication, and thus could be useful if CRS is related to active FHV-1 infection.
    • Some cats respond to glucocorticoids. Prednisolone (or prednisone) can be administered at 1 to 2 mg/kg per day. If benefit is seen within a week, the dose can be tapered to the lowest effective dose. When signs are controlled, oral glucocorticoids may be replaced by topical therapy using instillation of intranasal drops or glucocorticoids administered by metered-dose inhaler. Infectious cause of CRS should be ruled out before steroids are administered.
    • First-generation antihistamines, such as diphenhydramine, are not helpful, but newer, second-generation antihistamines may be beneficial.
    • Leukotriene inhibitors may be helpful.
    • Piroxicam is an antiinflammatory drug with potential benefit.
    • Some cats may benefit from nasal decongestants as oral medications or nasal drops. Nasal drops can cause profuse salivation and excitement, and frequent use should be avoided because of rebound congestion.
  • Clients should be warned that CRS is not a curable disease but rather a controllable chronic condition.

Surgery is generally reserved for cats that do not respond to medical management (Figure 1).

  • Severely affected cats may have hyperplastic mucosa lining the frontal sinus and obstruction of the nasofrontal openings. Secretions accumulate in the frontal sinus secondary to the outflow obstruction.
  • Advanced imaging techniques such as CT or MRI are recommended before any surgical intervention to assess the degree of mucosal hyperplasia and bony changes.
  • Insertion of drains into the frontal sinus and extending through the nasofrontal openings into the nasal cavity may aid medical management if obstruction of the nasofrontal opening(s) is documented (Figure 2).
  • Sinus obliteration should be considered only when all other treatments have failed. Sinus obliteration is a tedious procedure that requires strict attention to detail. The goal is to remove all the mucosa lining the frontal sinus, close the nasofrontal openings, and then fill the sinus with a material (typically fat grafts) to prevent reaccumulation of secretions in the nasal cavity.
    • Vascular ingrowth into the fat graft over time (6 to 12 months) results in obliteration of the sinus with fibrous tissue, bone, and viable fat graft.
    • Four of six cats in one clinical study had excellent results with significant improvement in the other two; follow-up times ranged from 14 to 22 months.
    • Periodic sneezing and nasal discharge were the common postoperative problems.

Nutritional Aspects
Cats with rhinosinusitis may be reluctant to eat. Feeding aromatic foods, including warmed canned foods, may help stimulate appetite.



  • Amoxicillin (10 to 20 mg/kg Q 8 to 12 H orally)
  • Amoxicillin-clavulanic acid (10 to 20 mg/kg Q 12 H orally)
  • Azithromycin (5 to 15 mg/kg daily for 5 days, then every third day orally)
  • Doxycycline (5 to 10 mg/kg Q 24 H orally; caution: may cause esophageal stricture. Ingestion of capsules should be followed by administration of water.)

Other Agents

  • L-lysine (500 mg per cat Q 12 H orally)
  • Glucocorticoids: prednisolone, (or prednisone) initially 1 to 2 mg/kg per day orally; then tapered. Steroid-containing ophthalmic or nasal drops (1 drop into each nostril Q 24 H)
  • Antihistamines: cetirizine (2.5 mg per cat per day orally)
  • Leukotriene inhibitors: montelukast (0.25 to 0.5 mg/kg Q 24 H orally), zafirlukast (0.5 to 1.0 mg/kg Q 12 to 24 H orally)
  • Piroxicam (0.3 mg/kg Q 24 to 48 H orally)
  • Decongestants: oxymetazoline or xylometazoline (1 drop each nostril once a day on occasion)


  • Disease severity and course vary from cat to cat.
  • Cats with worsening clinical signs or anorexia should be reevaluated. Nutritional needs should be addressed.
  • Appropriate viral vaccination before exposure will minimize the severity of FHV-1 or FCV infection.

In General

Relative Cost

  • Diagnosis is one of exclusion; proper evaluation includes imaging studies and histopathologic evaluation and can be costly ($$$$).
  • Medical therapies are not generally expensive ($).
  • Surgical therapy: $$$$$


  • Clinical signs can be controlled in many cases, but cure is rare.
  • Repeated, prolonged courses of antibiotics may help control clinical signs in many cats.
  • Surgical therapies are generally reserved for cats that do not respond to medical management.
  • The role of infectious agents, including viruses, deserves further study and clarification.


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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