Determining the right category of cough relies on clinical signs and diagnostic findings.
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:
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.
Some characteristics of a coughing dog
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.
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.
Selected features of coughing in dogs
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.
Second, the presence of a cough that can be induced with tracheal pressure does not indicate that the problem is tracheal or bronchial. Dogs with pulmonary parenchymal abnormalities, such as cardiogenic pulmonary edema, or even normal dogs, will cough with tracheal pressure.
Since a cough indicates an underlying respiratory problem, it is important to determine the nature of the problem before deciding on treatment.
With a purposeful cough, the treatment goal is to help eliminate the unwanted material from the respiratory system. Treatments to consider include antibacterials, nebulization and coupage (if bacterial pneumonia), medical management of the underlying cause if present (e.g., megaesophagus) and lung lobectomy if indicated (e.g., foreign body).
Additional diagnostic tests that may help establish the need for specific treatments include transtracheal wash, bronchoscopic examination and bronchoalveolar lavage and computed tomography (CT) or magnetic resonance imaging (MRI) of the thorax. A treatment that is contraindicated is the use of cough suppressants.
With a warning cough, treatment goals are to address the underlying problem before further deterioration and to provide emergent supportive care. Treatments to consider include oxygen supplementation for dyspneic dogs; diuretics in cases of cardiogenic pulmonary edema; crystalloid fluid therapy, plasma transfusion and vitamin K in cases of pulmonary hemorrhage due to anticoagulant rodenticide intoxication; anticoagulants (and possibly plasma transfusions or other therapies based on inciting factor) in cases of PTE; chemotherapy, radiation therapy, and/or surgical therapy for neoplasia; and surgical correction in cases of lung-lobe torsion.
Additional diagnostic tests that may help establish the need for specific treatments may include an echocardiogram and electrocardiogram (if cardiogenic pulmonary edema), prothrombin time (if anticoagulant rodenticide toxicity), platelet count, fibrin degradation products measurement, d-dimer assay, assessment of antithrombin III levels and possibly a lung perfusion scan or pulmonary arterial angiogram (if PTE is suspected) and thoracic ultrasound, CT, and/or MRI and needle aspiration or biopsy of thoracic masses. Contraindicated treatments include cough suppressants and expectorants.
With a nuisance cough, the dominant goal of treatment is comfort. Treatments to consider include cough suppressants (except if a secondary bacterial infection or ventilation problem is present), environmental modification (e.g., air purifier, avoidance of exposure to airborne infectious agents), weight loss if the dog is obese, bronchodilator drugs, and tranquilizers used on an as-needed basis if anxiety appears to play a role in triggering or sustaining the cough.
Additional diagnostic tests that may help establish the need for specific treatments may include transtracheal wash, bronchoscopic examination and bronchoalveolar lavage. A treatment that is contraindicated is the use of expectorants.
With a purposeful cough, the outcome depends on the ability to eliminate the source. Extraction of a foreign body generally carries a good prognosis, for example, whereas bacterial pneumonia caused by chronic aspiration associated with megaesophagus carries a guarded prognosis due to the high likelihood of recurrence.
More frustrating in terms of exact prognosis is the juvenile dog with pneumonia secondary to suspected viral or primary bacterial causes (e.g., canine distemper, Bordetella, etc.). These young dogs may clear the infection but have persistent regional compromises of local immune function, fostering variable degrees of reinfection. In such cases, the cough may move from purposeful, when pneumonia is present, to nuisance, when pneumonia is absent, and back again, for months or years.
The prognosis associated with a warning cough is directly related to two factors: (1) the speed with which the animal is brought for evaluation and the underlying problem is correctly diagnosed; and (2) the response to treatment for the underlying problem.
For instance, a dog with pulmonary hemorrhage from severe anticoagulant poisoning can have an excellent outcome if treated early and appropriately; the same dog may die if not evaluated and treated rapidly.
Nuisance coughs carry a fair prognosis. When caused by severe, worsening compromise of the airways (e.g., advanced cases of collapsing trachea or bronchial compression from cardiac enlargement), the prognosis is guarded. However, when nuisance coughs are not caused by such disorders, they can be treated on an as-needed basis and are compatible with a good quality of life.
Johnny D. Hoskins
Dr. Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine with specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: firstname.lastname@example.org.