Dr. Etienne Côté lectured on "Cough in Small Animal Medicine: A New Clinical Approach" at the 2006 American College of Veterinary
Internal Medicine (ACVIM) Forum in Louisville, Ky. Here are some relevant points:
Some characteristics of a coughing dog
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Coughing in dogs stems from many underlying respiratory disorders, ranging from processes that may rapidly become life-threatening
if not treated, to harmless disorders, to merely annoying disorders.
Cough is defined as a sudden, forceful expiratory effort, initially delivered against a closed glottis, which expels air from
the lungs and airways. It is a specific indicator of a respiratory-system problem.This stands in contrast to an increase in
respiratory effort or labored breathing, for example, which can be caused by primary respiratory disorders but also by pain
of any origin, metabolic imbalances, severe systemic illness or anxiety.
The problem is ...
Selected features of coughing in dogs
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In an attempt to classify coughs in small-animal medicine, veterinarians traditionally grouped coughs into various categories
based on clinical features. Extrapolated from human medicine, they include productive or nonproductive, moist or dry, inducible
with tracheal pressure vs. non-inducible, and daytime vs. nocturnal. Despite their longstanding existence, these categories
often overlap, making it frustrating and potentially misleading to try to identify an underlying cause based on these characteristics
alone.
The solution is...
A clearer and more treatment-oriented way of classifying a cough is to categorize it into one of three groups: purposeful
coughs, warning coughs and nuisance coughs. These groups have little overlap.
A purposeful cough is one that simply is beneficial: The expulsion of air and material from the respiratory system helps eliminate the underlying
problem. Two examples: bacterial pneumonia, in which the cough helps to expel pus; and an inhaled foreign body, in which the
cough may assist in expelling the foreign material.
A warning cough implies that the cough is one manifestation of a serious, often systemic, condition that needs immediate attention and which
may become life-threatening without treatment. Examples include pulmonary edema; pulmonary hemorrhage, such as that which
occurs with anticoagulant rodenticide intoxication; pulmonary or other intrathoracic neoplasia; pulmonary thromboembolism
(PTE); lung-lobe torsion; and severe cases of allergic respiratory disease.
A nuisance cough occurs because the cough reflex has been triggered unnecessarily by an abnormal influence, such as collapsing trachea, chronic
sterile bronchitis, tracheal or bronchial pressure due to cardiomegaly, uncomplicated infectious tracheobronchitis and mild
allergic respiratory disease.
Determining the right category relies on clinical signs and diagnostic findings.
Specific features of the physical examination include respiratory effort at rest (is it increased?), general demeanor (active
and responsive? sluggish? anxious?), mucous-membrane color (pink and moist? cyanotic/ashen?), heart sounds and pulse (normal?
heart murmur? gallop sound? other third-heart sound? irregular arrhythmia?), presence of respiratory sinus arrhythmia (which
makes cardiogenic pulmonary edema very unlikely, even in the presence of a heart murmur) and auscultation of all lung fields
for the presence or absence of normal breath sounds.
After the history and physical examination, a cornerstone of diagnosis in coughing dogs is thoracic radiographs. Further evaluation
typically depends on radiographic findings and the differential diagnosis within each category.
Two misconceptions often occur in veterinary practice and may contribute to misdiagnosis if not clarified.
First, the presence of crackles on pulmonary auscultation is not synonymous with the presence of pulmonary edema. Pulmonary
fibrosis and other similar disorders often cause crackles. Therefore, the history, the rest of the physical examination and
thoracic radiographic findings all should be considered before making a diagnosis of pulmonary edema.
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