Feline lower airway disease (Proceedings)

Definitions:

      - feline lower airway disease describes a somewhat heterogeneous group of conditions affecting the lower airways of cats

      - no consensus definitions in veterinary medicine

      - different authors use different terminology to describe them

      - asthma may suggest reversible bronchoconstriction, and predominantly eosinophilic inflammation

      - chronic bronchitis may be associated with neutrophilic inflammation

Predisposing factors:

      - city cats (higher incidence than cats from more rural environments)

      - smoking households (anecdotal)

      - severe respiratory infection during kitten hood

      - environmental allergens (e.g. House dust mite, pollens etc.)

History:

      - generally either chronic coughing and/or an acute onset of respiratory distress

      - seasonal variation (in some cats)

Physical examination:

      - may be normal in cats with chronic cough

      - may reveal moderate to severe respiratory distress

      - pronounced crackles or wheezes may be present on auscultation

      - predominantly expiratory dyspnea

Diagnosis:

      - Thoracic radiographs

           o Increased bronchial pattern

           o Hyperinflation

           o Right middle lung lobe collapse (occasionally)

           o May appear normal

           o Useful for excluding other causes of respiratory distress (e.g. CHF)

      - Lower airway cytology:

           o Samples can be obtained by various methods:

               ■ transoral / endotracheal wash vs. BAL (blind vs. bronchoscopic)

           o Eosinophilic inflammation (although other inflammatory cells may be present)

           o Rarely bacterial infection

      - Culture of lower airway fluid:

           o Some cats may have a secondary bacterial infection (particularly those with right middle lung lobe collapse)

           o Mycoplasma infection may also play a role in triggering an asthmatic response in some cats

      - Baermann fecal:

           o To evaluate for possible lung worm infection (Aelurostrongylus abstrusus); especially in young outdoor cats

           o Larvae may also be identified on a tracheal wash

      - Heartworm testing:

           o Antibody and/or antigen testing

           o Echocardiography is occasionally useful

           o Unfortunately diagnosis of feline HWD may be challenging due to a small worm burden

      - Routine blood tests:

           o usually normal

           o peripheral eosinophilia (> 1500 µL) may be present

*** It is important to realize that anesthetizing a cat with severe lower airway disease to obtain airway cytology may be stressful and exacerbate the respiratory status of the patient.

Technique to obtain 'blind' lower airway samples:

      - non-stressful placement of an intravenous catheter

      - pre-oxygenation for 5 minutes (oxygen cage)

      - induction with rapidly acting agent (e.g. Propofol or combination of diazepam + ketamine)

      - placement of sterile endotracheal tube

      - wash / lavage with sterile saline and collect fluid in a sterile cup or syringe

      - sample should be submitted for cytology and aerobic culture.

Treatment:

Long-term therapy tends to reflect both the owner and the clinician's preferences.

      - glucocorticoids

           o choices include anti-inflammatory doses of:

               ■ oral prednisone

               ■ inhaled corticosteroids (e.g. Fluticasone)

               ■ long-acting reposital preparations (e.g. Depo-Medrol®)

      - bronchodilators.

           o choices include:

               ■ theophylline

               ■ beta- 2 agonists:

                    • terbutaline

                    • inhaled albuterol.

               ■ novel treatments have also been proposed but currently there is no evidence to suggest efficacy in cats

      - fenbendazole:

           o I routinely deworm with fenbendazole to cover lung worm (and other GI parasites that could potentially aberrantly migrate through the lung and precipitate inflammation)

               ■ is used for treatment.

Specific treatment of status asthmaticus:

      - oxygen (usually in an oxygen cage)

      - minimal handling / stress reduction

      - beta-2 agonist bronchodilators (I prefer a nebulized albuterol trial)

      - anti-inflammatory doses of injectable rapid-acting glucocorticoids (e.g. Dex SP)

      - If a rapid response is not seen, it may be wise to re-consider the diagnosis

Prognosis:

      - individual cats vary in their response to various therapies

      - the prognosis is usually good, although some cats have recurrent bouts and require frequent medications.

Reference available upon request