Coughing and wheezing cats: Diagnosis and treatment of feline asthma (Proceedings)


Coughing and wheezing cats: Diagnosis and treatment of feline asthma (Proceedings)

Aug 01, 2010

Lower respiratory tract disease produces typical clinical signs in cats, including chronic cough and wheeze as well as dyspnea that may have a sudden onset.1 Owners may report an increase in respiratory rate (>30-40 breaths per minute), increased expiratory effort and lethargy. Clinical signs may be mild to severe and may be chronic or intermittent.

Differential diagnoses include heartworm disease2-3 , viral, bacterial or fungal infection, inhaled foreign body, cardiac disease, thoracic disease, neoplasia, and pulmonary parasites (ascarids, lungworms, lung flukes). Essentially, a diagnosis of feline asthma is a diagnosis of exclusion. Diagnosis involves a thorough history and physical examination as well as a minimum database (complete blood count, serum chemistries, urinalysis, and retrovirus serology). Other diagnostic tests for feline lower airway disease include thoracic radiographs, bronchoscopy and/or bronchoalveolar lavage with cytology and culture, feline heartworm serology, and fecal analysis. The most common radiographic abnormalities in cats with bronchial disease are bronchial and interstitial patterns, pulmonary hyperinflation and hyperlucency, aerophagia, and pulmonary soft tissue opacities.1,4

Feline Asthma

Feline asthma is one of a spectrum of conditions under the umbrella of chronic lower airway disease or bronchopulmonary disease that also includes chronic bronchitis. Feline asthma may also be called allergic airway disease or allergic bronchitis. There are important similarities between feline asthma and human asthma, and limited evidence suggests that some environmental allergens can cause disease in both cats and humans.5

Since feline asthma is characterized by airway inflammation and bronchoconstriction, therapy is aimed at reversing these changes. There are many treatments for feline asthma, including some experimental modalities borrowed from human medicine. Many of these treatments have not been well evaluated in the cat.

Treatment of Lower Airway Disease Patients with Acute Clinical Signs

Patients in acute respiratory distress may be unstable and should be examined and treated with great care. Some drugs may cause a temporary increase in heart and respiratory rate. When using combination drug therapy, be aware of the risk of arrhythmia in stressed, hypoxic cats. Some very anxious and stressed dyspneic cats may benefit from mild sedation with a low dose of acepromazine (0.05 mg/kg, IM, SQ).

First line therapy:
     • Supplemental oxygen: Preferably using an oxygen cage
     • Bronchodilators: Best via nebulizer or metered dose inhaler as the effects are seen within 5 minutes (versus 15-30 minutes by injection); give 2-4 puffs of inhaled drugs such as albuterol every 20 minutes; repeat injectable drugs in 15 minutes if required
     • Short-acting corticosteroid: Intravenous dexamethasone or prednisolone sodium succinate; may take 3-6 hours for maximum effect; useful in cats on chronic oral bronchodilator therapy to reverse down-regulation of airway β-adrenergic receptors causing drug tolerance

Second line therapy:
     • Anticholinergics: Atropine, glycopyrrolate; block vagal input causing bronchoconstriction and decrease bronchial secretions; not useful for long term therapy as these drugs will cause increased viscosity of airway mucus

Third line therapy:
     • Epinephrine: α- and β-agonist, can reverse bronchoconstriction; may cause arrhythmia

Treatment of Chronic Lower Airway Disease

Corticosteroids are the cornerstone of treatment for feline asthma as control of inflammation leads to clinical control.6 Inflammation exists even in the absence of clinical signs. Treatments can be combined to create tailored regimes. In general, the simpler and easier the treatment regime is, the more likely owner compliance will be achieved.

Feline asthma patients should be re-evaluated every 3 to 6 months and owners should be instructed to alert the veterinarian promptly if respiratory distress develops or the cat's clinical signs worsen.