Feline Asthma Syndrome

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Also known as Feline Allergic Bronchitis — Feline Bronchial Disease — Feline Bronchitis Complex

Introduction

Feline asthma is an allergic airway disease that bears many similarities with asthma in humans and with recurrent airway obstruction (RAO) in horses. Affected animals become allergic to allergens present in their immediate environment, including house dust mites and fungal spores and produce IgE antibodies against these molecules. When later exposed to the same allergens, asthmatic cats suffer a form of type I hypersensitivity response localised in the bronchi and bronchioles and resulting in constriction of the airways.

Extrinsic and intrinsic forms of the disease exist. The extrinsic form describes the formation of exudate in the airways and thickened airway walls. The intrinsic form describes the increased propensity for the bronchial smooth muscle to contract and lead to airway constriction.

Signalment

Most cats affected are young to middle-aged. Siamese cats are over-represented.

Clinical Signs

Chronic coughing is the single most common clinical signs of the disease.

Most cats have respiratory signs for several weeks or months prior to presentation. The signs tend to be recurrent, although some cats can present with acute onset respiratory distress without any prior signs.

Coughing may be paroxysmal and vary in intensity. Vomiting or retching may occur following the coughing. Some clients may complain that their cat is vomiting rather than coughing.

Respiratory distress can vary from tachypnoea to severe dyspnoea with expiratory wheezing.

Diagnosis

On physical examination: inspiratory and expiratory loud airway sounds can be auscultated. Duration of expiration is much longer than inspiration. An end-expiratory grunt may be heard as well as abrupt cessation of airflow near end expiration.

Expiratory wheezes are also common findings on physical exam. Cats may have a combination of expiratory wheezes, inspiratory crackles and loud respiratory sounds.

Occasionally, lung sounds may be quiet because of severe air trapping within the lungs, or on rare occasion, spontaneous pneumothorax.

Careful auscultation of the heart to differentiate cardiac disease from respiratory conditions is necessary.

Thoracic radiographs: Findings range from normal to increased bronchial and/or increased bronchial and interstitial patterns with or without alveolar densities. Peribronchial infiltrate is described as 'donuts' on the ventrodorsal view and 'tramlines' on the lateral view. There are often hyperlucent lung areas and flattening and caudal displacement of the diaphragm. There may be air trapping and hyperinflation. Atelectasis of the right middle lung lobe and mediastinal shift to the right have also been noted.

Rarely, rib fractures and pneumothorax may be evident.

Lung ultrasound, specifically VetBLUE, can be used to differentiate between wet lungs, dry lungs, and nodular patterns. Asthma will have dry lungs.

Haematology may reveal increased numbers of circulating eosinophils.

Bronchial cytology is variable, with predominant cell types including eosinophils, neutrophils and macrophages. However eosinophils can be found in normal cat airways.

Bronchial culture may reveal Mycoplasma species in approximately 25% of cases.

Heartworm antigen testing should be performed.

If the cat is presented in an acute episode, a rapid response to dexamethasone, bronchodilators and oxygen is highly suggestive of a diagnosis of asthma.

Treatment

Emergency therapy involves providing:

oxygen: indicated in any patient with respiratory distress
corticosteroids: prednisone, dexamethasone, inhaler
bronchodilator: terbutaline, or albuterol inhaler, epinephrine for extreme cases

Long-term therapeutic considerations:

Treatment depends on the severity and the persistence of clinical signs.

Eliminating any underlying inciting cause is important, such as changing or eliminating the litter, cleaning house vents, replacing filters, eliminating smoke, restricting the cat to certain areas of the house.

It is important to rule out parasitism, and a 7 day course of fenbendazole may be useful.

If heartworms are present they will need to be treated appropriately.

The primary method of control is the sustained use of glucocorticoids. Prednisolone can be given orally every 12 hours, and the dose can be tapered gradually to a dose every other day. Some cats may respond better to dexamethasone or triamcinolone. Sometimes cats can be weaned off the glucocorticoids and are then given only as needed by the owner.

Bronchodilators may reduce the dose of corticosteroid necessary to control clinical signs. Terbutaline or inhaled albuterol or salbutamol can be used.

Cyproheptadine and cyclosporin can be considered in cats which are resistant to other therapy.

Antibiotics should be administered if a bacteria or Mycoplasma species are isolated from bronchial culture.

Prognosis

Most cats respond favourably to oral therapy and can be controlled on low-dose, alternate day prednisolone. Untreated cats may develop irreversible chronic bronchitis and lung changes. Bronchiectasis can be a sequela of feline lower airway disease.

Many cats will develop additional acute episodes and owners should be instructed to seek immediate veterinary attention if these occur.


Feline Asthma Syndrome Learning Resources
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Small Animal Emergency and Critical Care Medicine Q&A 06


References

Lappin, M. (2001) Feline Internal Medicine Secrets Elsevier Health Sciences

Martin, M. (2005) Notes on cardiorespiratory diseases of the dog and cat Wiley-Blackwell

Macintire, D. (2005) Manual of small animal emergency and critical care medicine Wiley-Blackwell




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