Obstructive and allergic lung diseases affect many pets and are sometimes called asthma, bronchitis, or bronchial asthma. Unfortunately, these diseases are not easily classified and probably represent a variety of lung disorders. They do share a common finding of “hyper-responsive” airways.
When the airway is sensitive to certain stimuli, exposure to these agents leads to narrowing of the airways. The inciting agents are usually direct irritants to the airways or particles that provoke an allergic response in the respiratory tract. Regardless of the cause, the end-result is the same: muscle spasms in the bronchi (breathing tubes), buildup of mucus, and accumulation of cellular material. In particular, the inability to clear the bronchi of this material leaves the patient susceptible to secondary infections.
The animal is most stressed during the period of expiration. The difficulty with expiration is typical with obstructive disease of the lung. Air may become effectively trapped in the lungs, causing them to over-inflate. In some cases, this trapping leads to development of emphysema in the patient.
Obstructive lung disease is most common from 2 to 8 years of age. Female cats and Siamese cats seem to be more susceptible. Dogs do not get asthma as often as cats, but it can be a cause for coughing, particularly in older, smaller breed dogs.
Coughing and respiratory distress are the most commonly reported signs with obstructive lung disease. Coughing is a significant finding since there are relatively few causes of coughing in cats. Also, many patients assume a squatting position with the neck extending during these coughing episodes. Wheezing is easily heard with a stethoscope and is sometimes so loud that it can be heard without a stethoscope. Occasionally, sneezing and vomiting are noted.
As mentioned above, this group of diseases is characterized by hyper-responsive airways. The small breathing tubes (bronchi and bronchioles) can react to a number of stimuli, including:
- Inhaled debris or irritants – dust from cat litter, cigarette smoke, perfume or hairspray, carpet fresheners, and perfumes in laundry detergent
- Pollens or mold
- Infectious agents – viruses, bacteria
- Parasites – heartworms, lungworms
Several tests may be performed to achieve a diagnosis of allergic lung disease:
- Complete blood count, blood chemistries, fecal exam and urinalysis. These tests help to assess the general health of your pet and may provide clues as to the underlying cause. One particular type of white blood cell, the eosinophil, is commonly associated with allergic events and may provide support for a tentative diagnosis of asthma. Also, in certain geographic areas, special tests will be performed on stool samples for evidence of lungworms.
- Heartworm test. While this test is important for all dogs in all parts of the country, it is not indicated for all cats. In areas where heartworm is prevalent both indoor and outdoor cats may be at risk.
- Feline leukemia and feline immunodeficiency virus tests (cats only). These tests are helpful in determining the overall health of your cat.
- Thoracic radiography (chest x-ray). Characteristic changes in the lungs are common on x-rays. Also, the x-rays can be suggestive of heartworms in some cases.
- Bronchoscopy, cytology, and airway lavage (washing). Bronchoscopy is a procedure that allows us to look down the airways of the anesthetized patient with a fiberoptic scope. After a visual examination of the airway is completed, the lining mucus of the bronchi may be sampled with a small brush. The mucus can be examined under a microscope (cytology). Finally, a small amount of sterile saline can be flushed into the airways to retrieve samples of material from deep in the lung. This material can be cultured for micro-organisms and can also be carefully studied under the microscope. The sediment can be evaluated for evidence of lungworms.
In some cases, an underlying cause cannot be identified, despite a thorough diagnostic workup. Even when the underlying cause is not identified, many pets can achieve a reasonable quality of life with medical management.
Successful management of allergic lung disease employs several therapies.
- Any factors known to trigger or aggravate breathing problems should be avoided. In some cases, this may mean trying different brands of cat litter (cats only) and eliminating cigarette smoke from the cat’s environment.
- Bronchodilators: These drugs are used to open the airways and allow air to move more freely. They should be used faithfully and as directed to obtain maximum effect.
- Corticosteroids have a beneficial effect on decreasing inflammation, dilating the airway, and decreasing mucus production. In many cases, they are given daily. In animals that do not take tablets well, long-acting injections can be given. These drugs have potential for some side effects, but this is less of a problem in animals than in humans.
- Emergency treatment may employ bronchodilators, oxygen, rapid-acting glucocorticoids, and epinephrine. If your pet has heart disease, please inform the emergency veterinarian as epinephrine is best avoided.
Obstructive lung disease is usually manageable. Sometimes a “cure” may be achieved if a specific underlying cause can be identified and treated. Extreme respiratory distress constitutes an emergency, and, as with humans, your pet should receive immediate attention.