A number of different conditions may cause coughing episodes. Some of these conditions include inflammation and infection (bacterial, fungal, and viral) of the respiratory tract, foreign bodies or tumors within the respiratory tract, allergies, tracheal collapse, parasitic disease (including heartworm infections and lungworm infections), aspiration pneumonia, and underlying heart disease.
How do we determine what the underlying cause of the cough in my pet?
A complete history and physical examination of your pet will provide us with some clues regarding the cause of the cough. The pattern, characteristics, frequency and timing of the coughing episodes are important to note. For example, is the coughing noted only in relation to periods of exercise or is the coughing noted only at night when your pet is lying down?
A physical examination of your pet will include a through assessment of the respiratory tract and heart for evidence of abnormal breath and heart sounds.
A series of screening tests may provide us with some additional clues regarding the cause of the coughing episodes and will provide us with an overall assessment of your pet’s general health. However, these tests are unlikely to provide us with a definitive diagnosis; additional diagnostic tests are almost always needed in order to arrive at a definitive diagnosis for coughing, which will optimize treatment for your pet.
What might these screening tests include?
Depending upon your pet’s history and physical examination findings, these screening tests may include a complete blood count (CBC), a serum biochemistry profile, a urinalysis, a fecal flotation, a fecal Baermann, a heartworm test for microfilaria, and thoracic radiographs and/or ultrasound.
What could these tests indicate?
The CBC includes an evaluation of the red blood cells, the white blood cells, and the platelet components of a blood sample. Changes in the red blood cell components could include anemia associated with a chronic respiratory tract disorder. Alternatively, if the respiratory or cardiac disease is severe or long-standing, we may find evidence of increased numbers of red blood cells. Such increased red blood cell numbers would be the body’s way of trying to deliver oxygen to the tissues despite compromised lung or cardiac function.
The white blood cell numbers may be increased if inflammation or infection is a cause of your pet’s cough. Increases in specific types of white blood cells, for example eosinophils, may point to an underlying allergic or parasitic cause to the cough.
The serum biochemistry profile and urinalysis are not likely to provide us with definitive information regarding the underlying cause of the cough but secondary effects as a result of compromised organ function may be noted. For example, if your pet’s cough is due to underlying heart disease, then other organs will be affected by the compromised blood flow; this organ compromise may be reflected by increases in the kidney or liver related metabolites and enzymes.
A coagulation profile is indicated if bleeding is noted in association with the coughing episodes. A coagulation profile will evaluate the activity of the proteins involved in blood clotting.
A fecal flotation and a fecal Baermann test may be used to evaluate fresh fecal samples for the presence of eggs (using the flotation technique) or larvae (using the Baermann technique) from parasites capable of infesting the respiratory tract. Both tests are suggested if parasitic infection is suspected because some parasites diagnosed from eggs in the feces while others, such as the lungworm, are diagnosed from the presence of larvae in the pet’s feces. .
Heartworm (Dirofilaria immitis) testing may be indicated if your dog has not been receiving a heartworm preventative during the summer mosquito season, or if there has been recent travel to a geographical region that has a high incidence of heartworm disease. Heartworm testing typically involves a serum sample that is evaluated for the presence of a protein (antigen) specific for heartworm. If the results of this initial screening test are equivocal, then other confirmatory tests such as evaluation of a blood sample for heartworm microfilaria (immature heartworm) or chest radiographs, may need to be employed.
Thoracic radiographs, ultrasound and electrocardiograms may be used to evaluate the lungs and heart for evidence of masses, fluid accumulation, cellular infiltrates, or enlargement. Depending upon what changes are noted, further more invasive testing may be undertaken
What additional tests may be required?
Additional more invasive tests may include a transtracheal wash, a brochoalveolar lavage, a fine needle aspirate of accumulated fluids, a fine needle aspiration biopsy of mass lesions, and a bacterial culture of any harvested material
The results of the initial screening tests will determine what additional tests are indicated.
A brief review of the indications for these tests follows.
A transtracheal wash is indicated when the initial screening tests are supportive of upper airway disease. A transtracheal wash involves the infusion of a small quantity of sterile solution into the trachea (windpipe), where it will contact the lining and mix with any secretions and debris. This fluid is then quickly aspirated back into the syringe, with the aim of retrieving samples of airway secretions including cellular material and infectious agents (such as bacteria, fungi, or parasites) that will give us an indication of the cause of your pet’s cough.
The material retrieved in the fluid must be processed rapidly, and evaluated by a veterinary pathologist. Therefore this sample must be sent to a veterinary referral laboratory.
There are two ways of performing a transtracheal wash. The first method involves the passage of a special catheter through the skin and into the trachea prior to infusion of the sterile fluid. No anesthesia, other than a local block, is required with this method. The second method involves use of a general anesthetic and the placement of an endotracheal tube (a tube that we normally insert into the trachea during general anesthesia). A second catheter is then threaded down the endotracheal tube so that the sterile fluid can be infused and re-aspirated.
Depending upon the elements present in the collected airway secretions, we may be able to determine what the cause of your pet’s cough is. For example, the retrieval of large numbers of special white blood cells called lymphocytes is supportive of a viral infection, while large numbers of eosinophils is supportive of allergic airway disease or parasitic infections.
Bronchoscopy allows the evaluation of the major airways by use of a small diameter, flexible, fiberoptic endoscope. Bronchoscopy allows us to visually assess the airways for inflammation, hemorrhage, and some parasites, and will be indicated if the pet may have a structural abnormality of the airways such as a collapsing trachea.
Additionally, bronchoscopy is a way of collecting samples from the lower airways using the bronchoalveolar lavage technique. A general anesthetic is required for bronchoscopy.
Bronchoalveolar lavage is similar to a transtracheal aspirate in that a small volume of sterile fluid is instilled into the airways and then re-aspirated in hopes of retrieving material from airway secretions and lesions. The difference is that with bronchoalveolar lavage, the lower parts of the airways are sampled. Therefore this method is more suited for diseases located deeper within the lung tissue. The disadvantage is that a general anesthetic is required for this procedure. As with a transtracheal wash, the material we obtain from the bronchoalveolar lavage will be sent to a veterinary pathologist for assessment.
Depending upon the nature of the material obtained by either transtracheal aspiration or bronchoalveolar lavage, we may need to culture some of the material in order to definitively determine whether or not there are bacteria or fungi present.
Masses and fluids in the chest may be sampled by use of a fine needle aspiration technique. This technique may not require anesthesia, and may or may not require ultrasonic guidance, depending upon the type of lesion we are sampling. A small gauge needle is attached to a syringe, and either cells from a mass or free fluid from within the chest cavity are aspirated or withdrawn. This material is then sent to a veterinary pathologist for assessment. This technique may yield cellular material that is useful in providing a diagnosis for the cause of your pet’s cough. A mass may, for example, be composed of abnormal cells that are suggestive of cancer, or a fluid may contain evidence of inflammatory cells that are supportive of an underlying bacterial infection.