Bronchopulmonary disease in cats—is it really asthma? (Proceedings)
Feline bronchial disease goes under a multitude of names reflecting the considerable heterogeneity in anatomic locations as well as etiologies that may be involved.
Persistent tracheobroncheal irritation causes the chronic (>two months) cough that is easily elicitable on tracheal palpation, the hallmark of chronic bronchitis. Morphologic changes occur in the tracheobronchial epithelium and wall, resulting in airway inflammation: mucosal edema and thickening, epithelial metaplasia and cellular infiltrates with an increased production of mucus. This mucus is extremely irritating, resulting in a self-perpetuating process. When the irritation is occurring mainly in the small airways that are less than 2 mm in diameter, rather than cough being the main clinical finding, an expiratory wheeze predominates. As the airways become obstructed, the air becomes trapped within the alveoli resulting in a chronic obstructive pulmonary disease (COPD), with an abdominal thrust component to the respiratory pattern and, over time, resulting in a caudal displacement (or flattening) of the diaphragm. This patient may present in dyspnea with cyanosis rather than being brought in with a history of nocturnal wheezing or coughing. Clients may bring their cat in because of post-tussive retching or gagging misinterpreted as vomiting. It is the irreversibility of early changes at any stage along with the inherent progression that makes conclusive diagnosis and ongoing treatment so important.
From a different perspective, coughing may be due to tracheobronchial irritation, mucus secretion, accumulation, and bronchoconstriction. The result of this is airway narrowing, increased airway resistance, decreased air-flow, air exchange, hypoxemia, exercise intolerance, dyspnea with an increased respiratory rate. Potentially cor pulmonale or pulmonary hypertension could develop. The use of anti-tussives, is, however, contraindicated as the coughing itself is not detrimental and antitussive agents thicken secretions making it more difficult to clear the mucus.Etiology
Despite the fact that we may call bronchopulmonary disorders "allergic bronchitis", the underlying etiologies and mechanisms are unknown. There has not yet been evidence to show that the clinical signs are associated with an increase in pulmonary mast cells, histamine release or IgE production. The presence or absence of eosinophils in secretions is not adequate proof that the condition is "allergic" in origin. Numerous inflammatory conditions/agents may incite the condition. These may include viral respiratory tract infections or inhaled irritants such as dust, aerosols, second-hand smoke, incense, hoods on litter boxes trapping dust, forced air heating/cooling, open fireplace use, use of sprays (pesticides, carpet cleaners, perfumes, deodorizers, oil misters). Alternately, these may be "triggers" acting to cause exacerbations of a chronic underlying condition.
Classically it is the young adult cat who is affected with a preponderance of the Siamese breed being represented; however, any age or breed may develop bronchopulmonary disease.
Signs range from chronic coughing, retching or expiratory wheezing, (especially at night), to severe respiratory distress and cyanosis. It is important to note that cats can adapt to their disease state. Thus, any further compromise may be critical. This explains why some clients are not aware that their cat has been ill when they present for a "first" acute attack. Vomiting may be misinterpreted by clients when they witness retching after severe coughing, or may be secondary to aerophagia (from respiratory distress or pain) or gastrointestinal disease.
In most instances, the patient will be afebrile, bright and alert. Normal breath sounds may be present in mild cases; an expiratory wheeze may be ausculted over the lungs as the cat is trying to force air out of the smaller airways. This may be so marked that there is obvious abdominal thrust visible. Palpation of the trachea often results in a cough. As this loosens the mucoid secretions in the airways, post-tussive auscultation may detect some crackles. Note: if no breath sounds are heard at all in a patient, this reflects severe bronchoconstriction; this cat is probably cyanotic.