What is Asthma?
Asthma is a recurring respiratory compromise in which the lungs’ airways are constricted (narrowed). In this disease, the airways of the lung are inflamed plus they are extra reactive to stress or respiratory irritants, and the flow of air through the lungs is reduced sometimes or all the time.
In the disease, excess mucus forms, the airway walls swell with inflammation and can actually ulcerate, and finally the airway muscles go into spasm leading to constriction.
Airway constriction leads to inability to draw a deep breath, intolerance to exercise, coughing, and musical sighing sounds called “wheezes,” though not all these symptoms may be apparent at the same time. Sometimes a low-grade chronic cough is the only evident sign.
But that cough can turn into airway spasms and a sudden asthmatic crisis at any time, which is life-threatening. Treatment involves relieving and preventing airway constriction as well as removing environmental irritants such as cigarette smoke.
Is Feline Asthma the Same as Human Asthma?
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 diagnose asthma in people are shared by cats, yet we are still working out the mechanics of this syndrome in cats and have a great deal to learn.
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 yet if feline airways are also diseased all the time or if the actual airway structural changes occur only when there are clinical signs of distress.
How is the Diagnosis Made?
Because of the constricted airways, the actual volume of air this patient can move in and out of the lungs each breath is reduced. There is often a great deal of effort seen in the cat’s breathing. 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, assuming the cat is not in too much distress to hold still for this procedure.
Classically, this radiograph will show what is called air-trapping, meaning that the small airways have constricted so that inhaled 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.
It is possible to view the tiny airways in much higher detail on radiographs. This is partly because they are made more prominent because of the mucus and inflammatory fluid inside them (the doughnuts and tramlines, as mentioned below) 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 radiograph. The terms used for such airway appearance are doughnuts (when viewing the airway end-on) or tramlines (when viewing the airway from the side). You may hear your veterinarian use these terms and they are classical findings in airway disease.
Some Asthmatic Cats have Normal Radiographs
Since visible changes are not always evident on radiographs, which can lead to diagnosing asthma when it is not there. Indeed, diagnosing asthma can be complicated and it is famously under-diagnosed because up to 23% of asthmatic cats can have completely normal radiographs.
The coughing cat with normal chest radiographs poses a diagnostic dilemma. It is hard enough to sort out potential issues when there actually are radiographic changes as many conditions can mimic others.
Because of the nature of feline heart disease, where the heart muscle can thicken without the overall external shape of the heart changing, heart disease should be considered. In heartworm endemic areas, feline heartworm disease should be considered.
If the patient is thought not to have too high an anesthetic risk, a tracheal wash and/or bronchoscopy can be considered but often have indefinite results. CT (cat scan) imaging is emerging as a helpful diagnostic tool but it is not yet available in many areas.
Response to Therapy as a Diagnostic Test
One important asthma feature is that the airway constriction it engenders is reversible. In an emergency situation, a small dose of epinephrine (adrenalin) or terbutaline (which expands airways) can reverse an asthmatic crisis in as little as 15 minutes. Response to an injectable corticosteroid (such as dexamethasone) generally yields a positive response within 30 minutes.
Sometimes, diagnostic tests still leave room for question and you have to simply go with medical treatment for asthma and regard response to therapy as evidence that the diagnosis is correct. See below for list of medications commonly used in the long-term management of this problem.
It is crucial to realize that the underlying problem in the airway is inflammation. Inflammation is what is responsible for the constriction. To resolve the inflammation, corticosteroid medications have been the cornerstone of therapy. These can be given in pills, by injection, or more recently through a metered dose inhaler, which has less systemic side effects.
Usually treatment is started with either an oral corticosteroid such as prednisolone or a long-acting injection such as Depo-Medrol. These medications are relatively inexpensive and a good response to them helps confirm the diagnosis, as mentioned. At the same time these are started, an inhaled steroid is added which takes about two weeks to build in the respiratory tract. Again, there is much less potential for corticosteroid side effects with an inhaler.
If inhaled steroids are too costly, oral corticosteroids long-term can be considered but have many potential side effects. So, if using these, it is important to taper the dose over time so as to find the minimum dose needed to control symptoms. Work with your veterinarian to find the lowest oral dose possible.
Metered Dose Inhalers
Human asthmatics have enjoyed the benefits of portable inhalers for years. These handy 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:
- Cats cannot be told when to inhale.
- Cats tend to object strongly to the spray-puff delivered by the device.
Interestingly these same problems apply to human infants with asthma and a device called a pediatric spacer was invented for them. This tubular chamber is attached to the inhaler on one end and a face mask on the other. The inhaler is actuated into the spacer and the infant simply breathes in the spacer’s contents.
The discovery that the pediatric spacer could also be used for cats has solved the feline inhaler problem as well. The set up is the same as described above for young children and the cat takes 7 to 10 breaths from the face mask to be properly dosed. Corticosteroid inhalers, Flovent® being the most popular, are typically used twice daily long term while airway dilator inhalers such as albuterol-containing Proventil® or Ventolin® are used for flare-ups and cats in crisis.
Cats are generally started on a combination of oral prednisone and the metered dose inhaler and gradually switched to the metered dose inhaler.The AeroKat device shown above is a great way to have the inhaled medication delivered to your feline companion.
Are there other Treatment Options?
Other medications that might be helpful include:
Terbutaline (Brethine®) and theophylline are airway dilators commonly used in the management of asthma. It makes sense that if constriction is an important feature of this disease that eliminating constriction would be therapeutically helpful. Terbutaline is available orally or as an injectable.
Some veterinarians encourage owners to keep a bottle of injectable terbutaline at home in case of a crisis and show them how to give it. If you are interested in this, let your veterinarian know. Theophylline is an oral medication usually given once a day at bedtime.
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 sometimes tranquilization.
Minimizing irritants in the air is always helpful to an asthmatic cat.
- Do not allow cigarette smoke in the cat’s environment.
- Use dustless cat litter.
- Consider non-topical insecticides. No sprays, either.
- Regularly replace air filters at home.
It is important to realize that asthma can culminate in a respiratory crisis that can become life-threatening if ignored. If your cat begins to breathe with an open mouth or if you see excessive abdominal movement during breathing and the cat is not purring, you may have an emergency situation. Contact your veterinarian immediately.