Feline Asthma is a recurring respiratory compromise that occurs when the lung airways constrict either spontaneously or in response to stimuli that normally should not cause a reaction. Excess mucus forms, airways swell with inflammation and can ulcerate, and the airway muscles spasm leading to constriction. Airway constriction leads to inability to draw a deep breath, intolerance to exercise, coughing, and musical sighing sounds called wheezing. Not all of these signs need be observed; sometimes only a low grade chronic cough is the only sign but it should be remembered that an acute asthmatic crisis can arise at any time and can represent a life-threatening event.
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 certainly appears that all the diagnostic criteria needed to make the asthma diagnosis in humans are certainly shared by cats; still, 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 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 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 in position for this procedure. Classically, this radiograph will show what is called air-trapping. This means that the small airways have constricted such 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.
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.
But some asthmatic cats have normal radiographs?
Since visible changes are not always evident on radiographs this can lead to the diagnosis of asthma when it is not in fact present. Indeed, the diagnosis of asthma can be complicated and it is famously over-Eosinophils diagnosed because it is consistent with normal radiographs.
Procedures that retrieve cells from the lower respiratory tract may be helpful in patients with normal radiographs. Such procedures include the tracheal wash and bronchoscopy. The cell type of allergy known as the eosinophil is copious in the secretions of an asthmatic patient. But even this finding is made complicated since eosinophils occur in normal feline respiratory secretions. Further, parasitic infections such as lungworm and heartworm also lead to eosinophil-rich respiratory secretions, but hopefully other tests have been used to rule these infections out.
Response to Therapy as a Diagnostic Test
One important asthma feature is that the airway constriction in engenders is reversible. In an emergency situation, a small dose of epinephrine (adrenaline) 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.
Sometimes, diagnostic tests still leave room for question and one has 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.
How do our veterinarians treat Asthma?
It is crucial 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. In asthmatic humans, inhalers of corticosteroid medications have been especially helpful in delivering the benefits of these hormones without the burden of side effects. Recently, there have been some advances in using pediatric inhaler devices to aid in the administration of these drugs to cats.
In an acute episode, it may be necessary to sedate the cat to reduce the anxiety associated with the difficulty breathing. Administration of oxygen and injectable drugs to bring the attack under control can then be administered.
Other medications that might be helpful include:
Terbutaline (Brethine) and theophylline (Theo-Dur) are airway dilators commonly used in the management of asthma. It makes sense that if constriction is an important feature of this disease, eliminating constriction would be therapeutically helpful. Terbutaline is an inhalant or 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.
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.
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 steroids or who are having problems that preclude steroid use. Side effects of cyproheptadine include increased appetite and tranquilization.
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.
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 respiration and the cat is not purring, you may have an emergency situation. Contact our veterinarians immediately at (909) 980-3575.