Chronic bronchitis is a disease in dogs affecting the smaller airways that branch out from the trachea (windpipe).

Bronchitis can be acute (short duration) and associated with reversible changes in the structure of the airways or chronic (long duration, usually more than 2-3 months) and associated with permanent, irreversible changes in the airways.

Prognosis is variable with this disease. In most dogs, permanent damage to the airways has occurred and the disease cannot be cured. With proper medical management, clinical signs can usually be controlled and further damage to the bronchi can be stopped or slowed.

What is chronic bronchitis?

• Chronic bronchitis is a disease in dogs affecting the smaller airways that branch out from the trachea (windpipe). These branches, called bronchi and bronchioles, allow the transport of air into and out of the alveoli, the sites of oxygen exchange.
• Typically, inflammation within the airways results in excessive secretions that plug the airways. The end result is an impaired ability to bring oxygen into the alveoli for delivery to the rest of the body.
• Although the term “asthma” is occasionally used to describe this form of airway disease in dogs, this term is very misleading. Asthma, in people, specifically refers to the reversible constriction of muscle within the walls of the bronchi.
• Chronic bronchitis is associated with inflammation and swelling of the walls of the bronchi resulting in narrowing of the airways and obstruction or blockage of airways by plugs of mucus or other secretions. The inflammation of the airways is not reversible.
  
• Bronchitis can be acute (short duration) and associated with reversible changes in the structure of the airways or chronic (long duration, usually more than 2-3 months) and associated with permanent, irreversible changes in the airways. Bronchitis may be caused by bacterial infections, hypersensitivity  disorders (allergies), parasites (i.e., lung worms, heartworm), or chronic inhalation of airway irritants. In chronic bronchitis the underlying cause cannot be identified.

Pertinent Anatomy

• Take note of the larger tubes extending into lung tissue called the bronchi.
• The small airways in the white circle show the small bronchiole tubes and the clusters of alveoli (air sacs) that look like grape clusters

Signs

• The most common signs of chronic bronchitis include daily coughing, difficulty breathing, or wheezing for a duration of 2-3 months or longer.
• Episodes of coughing can mimic vomiting; you may think that your dog is vomiting when in fact your dog is having a coughing fit followed by retching.
• Some severely affected dogs may have extreme exercise intolerance. These signs are not specific for bronchitis and can also be seen with many other diseases including heart failure, pneumonia, and lung cancer.

Diagnosis

• To diagnose canine bronchitis, usually the first test is a chest radiograph (x-ray).
• The presence of radiographic changes of airway disease combined with a clinical history of a middle to older aged dog with cough on most days for a duration of at least 2-3 months may be sufficient to establish a clinical diagnosis of chronic bronchitis. However, bronchoalveolar lavage (BAL) may be recommended for some dogs. This procedure allows collection of fluid and cells from your dog’s lungs. These samples are sent out to a laboratory to determine what types of cellular changes are occurring in the lungs. If bacterial or parasitic infection is present, the results will help assist in determining what therapy might be most effective. Bronchoalveolar lavage does require anesthesia, so if the patient’s condition is critical, it may not be possible to do this procedure because of increased risk of death.

Treatment

• Any underlying disease (i.e., bacterial or parasitic infection) must be diagnosed and treated. Changes may be needed in the dog’s environment. Dogs with chronic bronchitis often have sensitive airways, and the inhalation of irritating particles from certain environments may worsen their condition. It is strongly recommended that their exposure to smoke (cigarette or fireplace), dusts (carpet fresheners, flea powder), and sprays (insecticides, hair spray, perfumes, and cleaning products) be eliminated or minimized.
• Two classes of medications are commonly prescribed; bronchodilators (theophylline, aminophylline, pentoxifylline, and terbutaline) and corticosteroids (prednisolone, prednisone, and methylprednisolone). Bronchodilators (in theory) help to dilate or open the airways by relaxing the muscles around the airway walls. The overall effectiveness of these drugs is minimal to nonexistent in most dogs. Common side effects of bronchodilators in dogs can include vomiting, nausea, restlessness and lethargy.
• Pentoxifylline is unique in that has antiinflammatory effects and may be effective in some dogs with mild disease.
• Corticosteroids are anti-inflammatory drugs that decrease the inflammation and swelling of the of the airway walls. These medications are most effective for treatment of chronic bronchitis. Side effects of corticosteroids may include increased appetite, increased urination, increased thirst, and anxiety (pacing, restlessness). Corticosteroid inhaler therapy is highly effective; however, patient compliance to this type of treatment is unpredictable.
             

Prognosis

• Prognosis is variable with this disease. In most dogs, permanent damage to the airways has occurred and the disease cannot be cured. With proper medical management, clinical signs can usually be controlled and further damage to the bronchi can be stopped or slowed. Periodic relapses of cough are not unusual and require treatment. Cough is often not entirely eliminated, but reduced in patients with chronic bronchitis.
• Some dogs with chronic bronchitis develop severe irreversible changes to the airways termed bronchiectasis. These dogs are highly susceptible to recurrent pneumonia. A sudden increase in cough in patients with bronchiectasis requires prompt evaluation and chest radiographs to determine whether pneumonia is present.