Clinical Vignette
A 12-year-old castrated Scottish terrier was presented for a 3-month history of cough. Physical examination revealed mild expiratory dyspnea, inducible cough upon tracheal palpation, and a grade III/VI systolic heart murmur with the point of maximum intensity at the level of the left apex. The remaining physical examination was unremarkable.
Problem Definition and Recognition
Coughing is defined as a sudden noisy expulsion from the lungs. Cough, especially productive coughs, may result in terminal gagging, which owners may confuse with vomiting and/or regurgitation.
Hemoptysis is the coughing up of blood from the lower airways. It may be difficult to distinguish hemoptysis from blood that has been regurgitated, vomited, or originated from the nasopharynx.
Pathophysiology
The function of coughing is to remove irritant material from the respiratory tract. Cough receptors respond to both chemical and mechanical stimuli. Given that the larynx, trachea, and bronchi are very sensitive to touch, foreign material and excessive amount of secretions can initiate the cough reflex. Although very few mechanoreceptors are found in the terminal bronchioles and alveoli, chemoreceptors are present in these locations. There are stretch and irritant/inflammatory receptors in the pulmonary interstitium.
Regardless of location, once the cough receptors are activated, afferent impulses pass via the vagus nerves to the cough center located in the medulla oblongata of the brain. The efferent neurons of the cough center, in turn, activate a coordinated sequence of events:
Regardless of the cause of the cough, the sudden airway compression caused by a cough may result in, or exacerbate, inflammation of the airway and perpetuate the cough response. This may be accompanied by degenerative changes of the respiratory epithelium and eventually involve the wall of the bronchi, resulting in bronchial collapse and/or bronchiectasis.
On the basis of the location of cough receptors, the origin for a cough can be categorized into three major anatomical regions: (1) upper airway, (2) lower airway, and (3) cardiovascular (Table 20-1).
Hemoptysis occurs secondary to vasculitis of the bronchial and/or pulmonary vessels, pulmonary hypertension, or an underlying hemostatic abnormality. Pulmonary artery thromboembolism is a potential complication of heartworm disease (dirofilariasis) in dogs and cats that may result in hemoptysis. Vasculitis can be caused by inflammation from an infectious agent or immune-mediated disease, neoplasia, or trauma. The causes of pulmonary hypertension are numerous and are listed in Table 20-2.
Primary and secondary hemostatic abnormalities are discussed elsewhere (see Chapter 54).
Minimum Database
History and Physical Examination
The signalment (age, breed, sex) may increase the likelihood of certain conditions. For example, young patients are more likely to have infectious etiologies, while elderly small breed dogs may have cough secondary to degenerative mitral valve disease (endocardio-sis), bronchitis, and/or collapsing airway disease. Coughing in cats is most often secondary to acute or chronic bronchitis associated with hypersensitive/reactive airway disease (asthma and heartworms) or from infectious agents—fungal (i.e., histoplasmosis), bacterial (Mycoplasma), protozoal (i.e., toxoplasmosis), or parasites (i.e., Aelurostrongylus). In our experience, coughing secondary to cardiac disease is rare in cats.
TABLE 20-2. Causes of pulmonary hypertension
| 1. Primary (idiopathic) |
| 2. Chronic alveolar hypoxia a. Bronchointerstitial lung disease b. Airway obstruction c. Hypoventilation—Pickwickian syndrome (morbid obesity) |
| 3. Chronic left-sided cardiac insufficiency |
| 4. Pulmonary thromboembolism a. Hypercoagulable states i. Antithrombin deficiency 1. Protein-losing enteropathy 2. Protein-losing nephropathy ii. Adrenal disease 1. Hyperadrenocorticism—exogenous or endogenous iii. Peracute disseminated intravascular coagulation 1. Bacteremia 2. Pancreatitis 3. Neoplasia 4. Trauma 5. Immune-mediated hemolytic anemia b. Heartworm disease |
The history should focus on the nature/timing of the cough, vaccination status, heart-worm prevention, change in environment (e.g., exposure to other pets, and travel), and presence/absence of systemic symptoms (e.g., anorexia, depressed mentation, dyspnea, and exercise intolerance). Although it may be difficult to ascertain clinically, nonproductive cough is usually associated with diseases of the upper airways; whereas productive cough suggests diseases of the lower airways. A “goose-honk” cough in toy breed dogs is typical of a collapsing trachea. Cough secondary to cardiovascular disease may be more severe in the evening hours (i.e., nocturnal cough/dyspnea) due to redistribution of blood flow from relaxed skeletal muscles to the heart, resulting in increased pulmonary venous pressures and interstitial or alveolar edema. Cough associated with bronchial disease is many times most severe in the morning because pooled bronchial secretions in the terminal airways are moved by increased airflow associated with activity and more forceful breathing. As these secretions are moved in the airways, they stimulate the cough receptors.
In patients with a history of improper vaccination, staying at a boarding facility, or exposure to other animals, the likelihood of infectious disease is increased; while heartworm disease should always be considered for animals (with or without outdoor exposure) in endemic regions. Inhaled allergens and pollutants may trigger strong inflammatory responses. Although the response may be a normal reaction to uncommon or new irritants and allergens, most likely the response is an exaggerated response to normal environmental irritants and allergens. Cigarette smoke, house dust, dander, molds, and pollens are the most likely culprits. A careful history is important in an attempt to identify the source of the irritant or allergen and either reduce exposure or eliminate it when possible. Lastly, systemic signs of illness are usually associated with lower airway and/or cardiovascular causes of cough (Table 20-3).
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