Feline Asthma: Investigation and Treatment

It is quite common for cats to present to veterinary clinics with a chronic cough or wheeze. The problem may be constant or just recur from time to time, and can range from mild to severe. Clinically the disease may resemble human asthma, but the term feline asthma can be misleading as there are a number of different possible causes. Here we look at what those underlying causes can be, and the different forms of treatment available to affected cats.

Cats usually present with one or all the following signs:

1. Coughing
2. Wheezing
3. Difficulty breathing

A minority of cases will have the classic human status asthmaticus, rapid onset breathing difficulty due to severe narrowing of the bronchi. Cats tend to be middle aged or older, and Siamese cats may be more prone than other breeds.

The Pathology

Little is known about the underlying causes or exacerbating factors in feline asthma. There may be an element of genetic predisposition. While chronic inhalation of airway irritants, such as smoking, has been shown to cause bronchitis in humans, this has not been studied in detail in cats. Likewise, allergens such as pollen, housedust mites, dander, fungal spores, dust and cat litter could all be implicated theoretically.

To return to the comparison with human asthma, when trying to understand the underlying causes it is important to differentiate between asthma (constriction of the bronchi), chronic bronchitis (oversecretion of mucus with a chronic cough) and COPD (chronic obstructive pulmonary disease). Asthma is reversible bronchial constriction caused by eosinophil cells, whereas COPD is irreversible bronchial constriction involving neutrophil cells.

The Differentials

There are a large number of possible diagnoses when a cat first presents with coughing or breathing difficulty. Here are some of the more important ones:

1. Pulmonary edema. Often due to severe heart disease.
2. Infectious bronchitis. This can be due to bacteria, viruses or parasites.
3. Pleural disease. Filling of the space between the lung and the chest wall with air or an effusion.
4. Cancer. This can be a primary lung tumor or metastatic spread.
5. Potassium bromide induced respiratory disease. A side effect from an anti-epileptic drug.
6. Idiopathic pulmonary fibrosis. Responds poorly to treatment.
7. Pulmonary thromboembolus. Lodging of a clot in a respiratory blood vessel causing sudden onset breathing difficulty.
8. Pulmonary hypertension. Usually secondary to other heart or respiratory disease.

Diagnosis

1. Clinical examination

The first step in the diagnostic protocol is a thorough clinical examination by a veterinarian. This should localize the origin of the disease to the upper airways, lower airways or pleural space. If the cat is found to have pleural disease, a needle may be inserted straight away to remove either air or a sample of the effusion for both diagnosis and short term treatment of the respiratory distress.

2. Radiography

The next test performed is usually thoracic radiography. This is best performed under general anesthetic so there is lee chance for motion blur, though in acute situations this is not possible. This is where the most meaningful information can be gained.

3. Bronchoscopy

Bronchoscopy allows visualization of the larger airways, and assessment for increased mucus and inflammation.

4. Tracheal wash

This involves injecting a small amount of saline into the trachea and immediately withdrawing it, and then examining the cells and debris harvested under a microscope.

5. Bronchoalveolar lavage

This is similar to the technique described above, but the catheter is inserted all the way into a lower airway before the saline is injected and withdrawn. This is therefore a good test for lower airway disease.

6. Lung biopsy

This is an invasive procedure that carries a significant risk to the patient. It is only indicated where diffuse cancer or extensive fibrosis is suspected, or in severe disease that responds poorly to treatment.

Treatment

The aims of treatment are as follows.

1. Eliminate any suspected infectious agents. This may be a sufficiently long course of antibiotics if bacterial infection is suspected, or a wormer such as fenbendazole if lungworm is suspected.

2. Remove or avoid airway irritants. The most obvious one is ensuring the cat has no contact with cigarette smoke, and purchasing dust free cat litter.

3. Removal or avoidance of potential allergens. House dust mite allergy must be excluded by spraying the house with an acaricidal product.

4. Chronic therapy for the underlying condition. For long term treatment of cats with feline asthma, a combination of steroids and bronchodilators are a popular choice. Steroids reduce the inflammation and lower mucus production, and can limit long term consequences such as fibrosis. Bronchodilators are most useful when there is airway spasm. Traditionally, medication has been given orally via tablets, but over the last few years, metered dose inhalers such as the ones used for human asthma have come on the market.

Aerosol therapy has the advantage that the maximum concentration of drug is delivered to the target site. This means that lower overall doses can be used, and the cat is less likely to suffer the negative side effects of steroids. Various inhalers can be used in both cats and dogs, but they tend to be designed for humans. As a result, higher doses are given compared with human medicine, as humans can be instructed to breathe deeply whereas cats will breathe normally at best.

Glucocorticoid drugs (steroids) used in inhalers include Beclometasone, Fluticasone and Budesonide. Beclometasone is cheap, but is rapidly absorbed into the bloodstream when you want it to hang around in the area where it applied. Fluticasone is more expensive, but tends to stay where you want it to. Budesonide is relatively inexpensive and though it is easily absorbed into the bloodstream, it tends to be removed the first time it goes through the liver.

Bronchodilator drugs used in inhalers include Salbutamol and Salmeterol. Salbutamol is very fast acting and therefore useful in a crisis caused by spasm of the bronchi. However, it only lasts for about 30 minutes and is therefore unsuitable for chronic therapy as frequent dosing is required. Salmeterol on the other hand is longer acting, and lasts for about 12 hours so twice daily dosing is possible. Salmeterol is better for long term control of mild to moderate asthma while Salbutamol is better for relief of acute bronchospasm.

The Seretide Evohaler is useful for cats requiring both steroid and bronchodilator therapy. It contains salbutamol and fluticasone, a combination allowing minimal dosing frequency.

Spacer devices

A spacer device consists of a chamber into which the aerosol drug is released at one end, with a mask at the other end which fits snugly over the cats mouth and nose. Human baby spacer devices (e.g. Babyhaler) can be easily adapted for cats. Alternatively, veterinary spacers specifically designed for cats are now on the market (e.g. Aerokat). The spacer should be held over the cats nose and mouth for about 30 seconds to ensure complete delivery of the drugs. It should be remembered that aerosol steroid therapy can take up to 2 weeks to reach full effect, and if the cat has been on oral steroids previously, these should be phased out slowly during these initial 2 weeks.

Is treatment lifelong?

Generally yes. Doses can often be reduced gradually once clinical remission has been achieved. As with many chronic conditions, complete control might not always be possible and an acceptable quality of life is the main aim of the treatment.