Asthma is a recurring respiratory compromise that occurs when the lung airways constrict either spontaneously or in response to stimuli. Excess mucus forms, airways swell with inflammation and can ulcerate, and the airway muscles go into spasm leading to constriction. Airway constriction leads to inability to take a deep breath, intolerance to exercise, coughing, and wheezing. Not all of these signs need be observed. An acute asthmatic crisis can arise at any time and can represent a life-threatening event.

The exact causes of feline bronchial asthma are not known. The suggested cause in most cases is allergy. Allergies can develop to many things such as pollens, molds, foods, dust, and chemicals that are inhaled. Therefore, testing for environmental allergies and ruling out food allergies may be considered.

The allergic reaction within the body causes a narrowing (constriction) of the small air passages within the lungs. This results in a lack of air being able to get into the lungs supplying oxygen to the body. Recurrent attacks are common. Time between attacks varies greatly. There is no way to predict when or how severe the attack will be. However, the earlier we are able to treat the condition, the quicker the recovery. Veterinary treatment will be required once signs begin to develop.

The feline condition was named "asthma" due to the clinical features shared with the human disease. As of this time, it appears that all the diagnostic criteria needed to make the asthma diagnosis in humans are shared by cats. For example, in humans we know that while actual symptoms of asthma occur in episodes, the airways of the lung are diseased all the time. We do not know if feline airways are also continually diseased or if the actual airway structural changes occur only when there are clinical signs of distress.

During an asthma attack, the actual volume of air the patient can move in and out of the lungs during each breath is reduced. There is often a great deal of effort seen during an asthmatic cat’s breathing pattern. The abdomen appears to be working to push air out and the breaths are shallow and rapid. The cat may even be breathing with its mouth open in an effort to move the largest possible amount of air.

The next step toward making a diagnosis of feline asthma is the chest radiograph. With feline asthma, this x-ray will show what is called "air-trapping." This means that the small airways have constricted such that inspired air cannot be exhaled. The lungs are larger in appearance than normal as they are over-inflated. The diaphragm may seem flattened due to this over-inflation.

Figure 1.		Figure 2.
Both these radiographs are from the same patient. Figure 1 is normal. Figure 2 was taken during an asthma attack.

In Figure 2, it is possible to view the tiny airways in much higher detail. This is partly because they are made more prominent because of the mucus and inflammatory fluid inside them and partly because they are surrounded by more air than usual (air-trapping).Inflammation and mucus build up within the airways causing their walls to appear thickened in the Figure 2.

However, visible changes are not always evident on radiographs. Procedures that remove cells from the lower respiratory tract may be helpful in patients with normal radiographs. Such procedures include the transtracheal wash and bronchoscopy. The cell type called "eosinophils" can be found in large numbers in the secretions of an asthmatic patient. Tracheal and lung secretions may also be cultured. It is important to rule out other disorders such as infection, heartworm disease, cardiac disease, lung worms, and other pulmonary parasites, cancer and pleural diseases.

Sometimes, diagnostic tests will turn out equivocal and veterinarians regard response to therapy as evidence that the diagnosis is correct. If the animal’s airway constriction is reversible with asthma treatments then they may have asthma. In an emergency situation, a small dose of epinephrine (adrenalin) can reverse an asthmatic crisis in as little as 15 minutes. Response to injection with an airway dilator such as terbutaline usually occurs within 30 minutes. Response to a long acting corticosteroid injection (such as methylprednisolone acetate/depomedrol) generally yields a positive response within 48 hours.

It is important to realize that the underlying problem in the airway is inflammation. To resolve inflammation, corticosteroid medications such as prednisone are necessary; doses are frequently high and continued long-term. Cats are relatively resistant to steroid side effects and long term oral use is generally not problematic.

Another method commonly used besides long-term oral use of steroids is periodic use of injectable long acting corticosteroids. This is generally an injection given periodically when the cat seems to be showing signs of respiratory discomfort. This is more convenient for many pet owners than trying to administer daily pills.

In asthmatic humans, inhalers of corticosteroid medications have been especially helpful in delivering the benefits of these hormones without the burden of side effects. Such delivery systems have recently been developed for feline use and are very effective.

Human asthmatics have enjoyed the benefits of portable inhalers for years. These devices deliver medication locally to the airways, thus minimizing drug side effects to the rest of the body while maximizing desired response.

There were two problems with using these devices in cats: 1) Cats cannot be told when to inhale and 2) Cats tend to object strongly to the spray-puff delivered by the device. However, asthma medications have recently been designed to be used with a nebulizer. The nebulizer is attached to a small face mask and the medication is continuously aerosolized. When the cat breathes the asthma medication is respired and begins taking effect immediately. The whole process takes about 10 minutes and is not stressful for the cat.

Other medications that might be helpful include:

Airway Dilators: Terbutaline (Brethine) and theophylline (Theo-Dur) are airway dilators commonly used in the management of asthma. Terbutaline is available for humans as an inhalant and an injectable.

Antihistamines: Histamine is an inflammatory substance released during allergic response. Histamine has been thought to be involved in the airway constriction mechanism and antihistamines are widely prescribed to asthmatic cats. Recent research, however, indicates that a special receptor in the feline airway (called an “H3”) receptor leads to a dilation response to histamine instead of a constriction response. This could be why antihistamines have not been found to be of dramatic assistance in the management of feline asthma. More research in this area is currently needed.

Cyproheptadine: One of the biochemicals involved in the asthma inflammation cascade is called “serotonin.” It is directly involved in constriction of the airways in cats. Cyproheptadine is an anti-serotonin medication with concurrent antihistamine properties. It is often used in cats who need extra help beyond their steroids or who are having problems that preclude steroid use. Side effects of cyproheptadine include increased appetite and tranquilization.

Zamflurkast (Accolate): This new medication has received a lot of attention in the human medical arena. It is meant to supplement other treatments and perhaps reduce the “requirement” of steroids needed to manage asthma. It is in the experimental stage for use in cats.

Cyclosporine: The use of cyclosporine in asthma is relatively new. Cyclosporine is an immunomodulator often used in organ transplant patients. It is very expensive and is generally reserved for asthmatics who have not responded to other treatments.