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What is Asthma and Bronchitis?
Please understand the following information is offered as a courtesy and is not intended to provide a diagnosis or medical recommendation for your pet.
Obstructive and allergic lung diseases affect many dogs 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” (over-reactive) airways.
When the airway of the dog 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 things which 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 dog susceptible to secondary infections.
The dog is most stressed during the period of expiration (forcing air out of the lungs). The difficulty with expiration is typical with obstructive disease of the lung. Air may become effectively trapped in the lungs, causing them to overinflate. In some cases, this trapping leads to development of emphysema in the dog.
Are some dogs more likely to get asthma?
Obstructive lung disease is most common in dogs from two to eight years of age.
What are the clinical signs?
Coughing and respiratory distress are the most commonly reported signs with obstructive lung disease. Wheezing is easily heard with the stethoscope and is sometimes so loud that it can be heard by the owners. Occasionally, sneezing and vomiting are noted.
What causes asthma?
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, such as:
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Inhaled debris or irritants - dust from cat litter, cigarette smoke, perfume or hairspray, carpet fresheners, and perfumes in laundry detergent
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Pollens or mold
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Infectious agents - viruses, bacteria
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Parasites - heartworms, lungworms
How is asthma diagnosed?
Several tests may be performed to achieve a diagnosis of allergic lung disease in the dog.
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Minimum data base (complete blood count, blood chemistries, fecal exam and urinalysis). These tests will help to assess the general health of the dog 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 some dogs, special tests will be performed on stool samples for evidence of lungworms.
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Heartworm test. This is not indicated for all dogs, as heartworms are rare in some parts of the country. In areas where they are common, however, strictly indoor dogs are still at risk.
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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.
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Tracheal wash, cytology and airway lavage (washing). Tracheal wash is a procedure which allows the veterinarian to collect material from the lower airways. 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 dogs can achieve a reasonable quality of life with medical management.
Some owners decline the complete workup for a variety of reasons. In such cases, it may be acceptable to treat the dog with a course of corticosteroids (“cortisone” or “steroids”) since most asthmatic dogs respond very favorably to these medications without significant side-effects. However, this approach may create two problems. Corticosteroids can complicate the management of dogs harboring secondary bacterial infections; therefore, prophylactic antibiotics are reasonable in cases where a workup cannot be performed. Dogs with heartworms often cough like dogs with asthma and will respond temporarily to corticosteroids. Therefore, dogs in locations where heartworms are common in dogs may be misdiagnosed as having asthma.
How is asthma treated?
Successful management of allergic lung disease employs several therapies.
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Any factors known to trigger or aggravate breathing problems should be avoided. In some cases, this may mean trying different brands of cat litter, eliminating cigarette smoke from the home, etc. The previous list (see “Causes”) details some factors which should be considered. It is important to pay close attention to environmental factors which may aggravate the condition.
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Bronchodilators. These drugs are used to open up the airway and allow the dog to move air more freely. They should be used faithfully and as directed to obtain maximum effect.
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Corticosteroids. Steroids have a beneficial effect on decreasing inflammation, dilating the airway, and decreasing mucus production. In many dogs, they are given daily. When the dog’s temperament is a concern, long-acting injections can be given as an alternative to pills. These drugs have potential for some side-effects and should not be withdrawn abruptly.
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Emergency treatment may employ bronchodilators, oxygen, rapid-acting glucocorticoids, and epinephrine. If your dog has heart disease, the attending veterinarian should be advised since epinephrine is best avoided.
Will my dog recover?
Dogs with obstructive lung disease are usually manageable. Sometimes “cure” may be achieved if a specific underlying cause can be identified and treated. Extreme respiratory distress constitutes an emergency and the dog should receive immediate attention.
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