What’s that noise your dog is making?  Why, it’s a cough, of course.  Yet, there may be some situations where the forceful noise produced by the dog is so bizarre that everyone is perplexed, including the veterinarian. 

A cough is defined as a sudden noisy expiration or explosion of air that usually follows an exaggerated effort to breathe in.  The mouth will open, unlike a sneeze, where the mouth is usually closed.  Then there’s that weird event, when the dog makes a lot of noise but doesn’t seem to sneeze: a reverse sneeze.  A reverse sneeze is associated with noisy inspiratory and expiratory events without the big expiratory burst.  Some dogs with nasopharyngeal disease may cough, sneeze and reverse-sneeze, as well as gag or retch, making it challenging for the veterinarian to figure out exactly what the problem is. 

The causes of cough are many and varied, but most can be traced to some stimulation or irritation of sensory nerves in the throat, windpipe or smaller airways.  The character of the cough may help to localize the problem to a specific area of the respiratory tree or cardiovascular system and to suggest its potential severity.  The duration of the cough is an important part of the history, as well as vaccination and heartworm status, travel or boarding history, pre-existing health problems, concurrent medications, and any prior history of cough. 

These factors are important because they can help the veterinarian determine the likelihood of certain kinds of cough.  The environment is also important.  For example dogs that live in an urban environment or with smokers are more likely to develop chronic small airway disease then are outdoor dogs, who may be more at risk for parasites, fungal infections, and allergies to trees, pollens and grasses. 

When coughing is a sign of disease

Some types of coughs are more troubling than others.  For example, coughs that are more noticeable at night tend to be associated with fluid retention in gravity-dependent areas of the lungs, as occurs with congestive heart failure.  Mitral valve and tricuspid valve degeneration are exceedingly common among small to medium sized aging dogs.  When the valvular insufficiency becomes severe and the heart enlarges substantially, then filling pressures on the left side of the heart rise.  If they exceed the forces that tend to return fluids to the left atrium of the heart, then fluid will leak into the lungs as pulmonary edema.  Congestive heart failure will commonly cause a soft nocturnal cough that may become productive and more continuous as the condition progresses.  The fluid produced often resembles watery, pink foam.  This type of cardiac cough usually worsens with exercise and is often associated with noticeable increases in breathing effort, even respiratory distress. 

Cardiac enlargement that is not associated with heart failure can also contribute to coughing because of the compression of large airways.  The point at which the trachea branches into the right and left bronchi is particularly susceptible to pressure from the enlarging left atrium.  Collapse or narrowing of this area stimulates a dry, harsh to honking cough that is also observed in patients with spontaneous collapse of the trachea or mainstem bronchi. 

Tracheal collapse is very common among toy breed and miniature-breed dogs.  The tracheal anatomy is supported by C-shaped rings of cartilage that are subject to degeneration and collapse.  The flaccid trachea changes diameter with different phases of breathing which frequently elicits a dry cough, especially repeated cycles of episodic cough.  The classic "goose honking" cough of tracheal collapse may become productive as the disease progresses.  The coughing is frequently exacerbated by tugging on the leash or by irritants in the air, such as perfumes, smokes or powders.  While the underlying anatomic problem cannot be corrected, there are medical and surgical strategies to minimize the cough and respiratory obstruction that is produced. 

Other dry coughs are associated with tonsillitis or tracheitis/tracheobronchitis, such as the familiar kennel cough.  Harsh noises are more often associated with airway problems than with lung or cardiac problems.  Coughs occurring because of allergic or cancerous conditions are frequently dry and nonproductive. 

Dogs with bacterial pneumonia will usually have a soft, productive cough that reflects the presence of mucus and purulent material within the airways.  The productive nature of a cough can be difficult to ascertain because most dogs will swallow the material that is coughed up.  An astute owner may note that the dog swallows or retches after coughing.  Patients with pneumonia frequently are systemically ill, with fever, poor appetite and lethargy, as well as cough, nasal discharge, and varying degrees of respiratory distress. 

Pulmonary vascular disease associated with arterial blood clots may result in the coughing of blood, a condition termed hemoptysis.  Dogs with hyperadrenocorticism, pancreatitis, immune mediated hemolytic anemia or heartworm disease are at increased risk for pulmonary thromboembolism that may cause bloody fluid or frank blood to exude into the airways. 

Patients with lung cancer, systemic bleeding tendency, or severe inflammatory diseases may also cough up blood.  Such patients should be seen immediately by their veterinarian or an emergency clinician; potentially, this is a very serious problem.  The patients’ overall health history, potential exposure to rodenticides, and heartworm status will be quite important to their assessment.  Fortunately, hemoptysis is a fairly uncommon problem. 

In contrast, the most common cause of chronic coughing in middle-aged to older dogs may well be chronic bronchitis.  Technically this label should be reserved for patients that have been coughing for two months without a discernible cause.  Chronic inflammation of the airways leads to wall thickening and mucus accumulation, with plugging of the small airways.  The resulting cough frequently sounds dry or harsh, but is frequently associated with gagging or retching after the cough because of fluid within the airways. 

The underlying cause of chronic bronchitis is unknown and treatments are aimed at minimizing the clinical signs of cough.  Inflammation and mucus production are treated with corticosteroids.  Bronchodilators and cough suppressants are frequently used concurrently.  Unfortunately, the condition tends to progress, leading to sacculation and gross distortion of the bronchi (termed bronchiectasis) in some, or other irreversible changes in airway function or anatomy.  Ultimately the condition may cause stress on the right side of the heart, predisposing the patient to heart failure.  Obesity and some genetic factors appear to influence the likelihood of this problem. 

Attempting diagnosis

After assessing the history, character of the cough, and physical examination findings, the veterinarian may elect conservative management of acute or chronic conditions, unless the dog is distressed or cyanotic (blue) from poor air exchange.  Patients that are coughing blood or are believed to be experiencing heart failure are also likely to be hospitalized, for diagnosis and treatment. 

X-rays of the chest (and possibly the throat) are the most specific tools for assessing the coughing dog.  Patterns seen on x-rays may suggest the likelihood of cardiac disease or disease of the lungs or airways.  It is reasonable to expect that x-rays may be repeated over time to assist in assessing the patient’s response to treatment or to evaluate a suspicious area or mass. 

Heartworm tests are likely to be performed if the patient’s records aren’t current, and a fecal examination may be ordered to look for parasite eggs.  Reviewing the white blood cell count is helpful, but will rarely lend specific diagnostic information.  If the neutrophilic fraction of the white blood cells is increased, then bacterial or fungal pneumonia may be more likely.  Increased numbers of eosinophils are suggestive of allergic or parasitic conditions.  Occasionally fungal or other infectious organisms can be seen within circulating white blood cells, rendering a specific diagnosis of the cause of cough. 

Thoracic ultrasound is especially useful in evaluating the structures and function of the heart.  Mass lesions that contact the side of the chest may be imaged with ultrasound.  If the lungs are surrounded by fluid, sonography may be quite useful; however, this technique is of limited valued for assessing the lungs or airways.  If pleural fluid is present it may be retrieved for analysis with a needle introduced into the chest cavity. 

Fluid within the lungs and airways must be sampled differently.  Tracheal or bronchial lavage procedures can be used to retrieve fluid and cellular samples for microscopic inspection and bacterial culture and susceptibility.  Fiberoptic imaging will permit visualization of the airways and specific sampling of masses.  Rarely foreign objects are retrieved. 

Often a therapeutic trial will be elected prior to invasive or expensive tests, but this approach may not be appropriate for all coughing dogs.  A particular dilemma is the chubby geriatric toy breed dog with collapsing trachea, mitral valve insufficiency and probable chronic bronchitis.  Small changes in the environment or activity of the pet may cause a worsening of cough that could be caused by a multitude of factors.  Subtle changes in chest x-rays or in response to medication changes will often direct the course of treatment. 

The importance of patience

Coughing may not sound like a serious problem, but sometimes it is a sign of a significant disease.  Since there are so many possible causes of coughing in a canine, it’s important for you to be patient as your veterinarian tries to get to the bottom of it all.  Many of the diseases associated with various types of coughing can be managed if they’re caught early on.