FELINE ASTHMA

 
(original graphic by marvistavet.com)

WHAT IS ASTHMA?

Asthma is a recurring respiratory compromise featuring the constriction (narrowing) of the lung’s airways. There are three features defining asthma:

• Airway inflammation
  
  
• Airway hyper-responsiveness
  
  
• Reduced airflow (which is at least partly reversible)

In English this means, the airways of the lung are inflamed plus they are extra reactive to mental stress or respiratory irritants, and the flow of air through the lungs is reduced (either sometimes or all the time). When all three features are present, we can be comfortable diagnosing asthma.

WHAT EXACTLY IS HAPPENING IN THE LUNGS WITH ASTHMA?

First, excess mucus forms in the airways. After that, the airway walls swell with inflammation and can actually ulcerate. 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 it should be remembered that a sudden asthmatic crisis can arise at any time and can represent a life-threatening event. Asthmatic airway constriction can happen spontaneously, in reaction to stress or anxiety, or as a type of allergic reaction. When it comes to treatment, relieving and preventing airway constriction is what it is all about.

IS FELINE ASTHMA THE SAME AS HUMAN ASTHMA?

The feline condition was named asthma because of 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, yet we are still working out the mechanics of this syndrome in the cat 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, as demonstrated in the animation above. 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 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.

 Radiograph of an asthmatic cat during an attack
(Photocredit: Darlene House B. Sc, DVM - used with permission)

In the radiograph above, 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 (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.

 Both these radiographs are from the same patient. The left radiograph is normal.
The radiograph on the right was taken during an asthma attack.

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 there. Indeed, the diagnosis of 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 deemed not to have too high an anesthetic risk, tracheal wash and/or bronchoscopy can be considered but are often ambiguous in results. CT ("cat scan") imaging is emerging as a helpful diagnostic tool but it is not 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 (an airway dilatory) 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 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.

TREATMENT OPTIONS 

ORAL AND INJECTABLE STEROIDS

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 medication actuation (the spray-puff delivered by the device). Interestingly these same problems apply to human infants with asthma and for them a device called a pediatric spacer was invented. 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.

(Photocredit: Trudell Medical International, used with permission)

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

Cats are generally started on a combination of oral prednisone and the metered dose inhaler and gradually maintained on only the metered dose inhaler.

Pediatric equipment is generally available from most human pharmacies, however, a device created specifically for feline use can be ordered. It comes with the spacer and an appropriately sized face mask. Your veterinarian will need to prescribe the metered dose inhaler usually from a regular human pharmacy.

To buy the Aerokat device, please visit:

www.aerokat.com

ARE THERE OTHER TREATMENT OPTIONS?

Other medications that might be helpful include:

Airway Dilators: 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.

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 sometimes tranquilization.

Cyclosporine: The use of cyclosporine in asthma is relatively new. Cyclosporine is an immunomodulator often used in organ transplant patients. It has been used occasionally in cats where adequate suppression of inflammation has not been possible with combinations of the other medications listed or when the cat is unable to take corticosteroids for other reasons (concurrent diabetes mellitus, infection, history of calcium oxalate bladder stones etc.) Cyclosporine should not be prohibitively expensive since cats, being small, require relatively small doses but blood levels of cyclosporine may be periodically recommended which increases the expense of this treatment significantly.

Allergen Specific Immunotherapy: Since allergy is generally a part of the asthma picture, it makes sense that "allergy shots" might be helpful. In fact, they are helpful to many cats. It is important to realize that this form of therapy takes months before benefits are obvious so it is not a method for fast relief but more for the "bigger picture." The owner must be able to give injections to the patient at home regularly. A veterinary dermatologist is generally needed to oversee this type of therapy.

DON’T FORGET...

Minimizing irritants in the air is always helpful to the 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 respiration and
the cat is not purring, you may have an emergency situation.
Contact your veterinarian immediately.

For more details including video on the use of the inhaled system we recommend visiting www.fritzthebrave.com which was set up by one family devoted to their asthmatic cat. It has grown into a detailed instructional site for both pet owners and veterinarians interested in the details of inhalers for feline asthma treatment.

Page last updated: 8/14/2022