Therapy for feline bronchopulmonary disease (asthma) (Proceedings)
Feline asthma is one of the most common bronchopulmonary diseases in cats and is responsible for substantial morbidity and occasional mortality. It is an IgE mediated hypersensitivity response against what otherwise would be harmless environmental aeroallergens. Exposure to an allergen allows for production of allergen-specific IgE formation. Those IgE antibodies then bind to mast cells on respiratory mucosal surfaces. Upon re-exposure to allergen, IgE on the surface of the mast cell bind allergen and send an intracellular signal to trigger mast cell degranulation. Mediators that are either immediately released from granules or later synthesized within mast cells are major contributors to signs of asthma. Inflammation in the airways leads to cellular infiltration (mostly eosinophils), increased mucus production, bronchoconstriction, and creates permanent architectural changes in the lung called airway remodeling. All of these lead to clinical signs of asthma.
Clinical presentation of the asthmatic cat
Any cat may have asthma, although it is most commonly diagnosed in young to middle aged cats and may be more common and/or severe in Siamese cats. Typical clinical signs include some combination of coughing, wheeze, and intermittent respiratory effort or distress. Signs are often slowly progressive but can cause severe bronchoconstriction and sudden dyspnea. Differential diagnosis for respiratory distress include congestive heart failure or pleural effusion, while differential diagnosis for cough include pulmonary parasites and infectious or non-infectious bronchitis.Although routine blood, urine, and fecal tests help evaluate overall health and rule out other disease, radiography and airway lavage are the most useful tests. Peripheral eosinophilia is common (~20%) but non-specific. Asthma cannot be ruled out because of normal thoracic radiographs but many cats have some combination of a bronchial lung pattern and evidence of hyperinflation (eg, increased lucency or flattening and caudal displacement of the diaphragm). Airway lavage typically demonstrates increased numbers of eosinophils and sometimes neutrophils. Lavage samples should be cultured (including Mycoplasma). Heartworms can cause a very similar clinical picture even in the absence of mature worms, but unfortunately diagnosis of feline heartworm associated respiratory disease (HARD) is very difficult and no specific therapy is available even if the condition could be recognized.
Therapeutic options for feline asthma
Therapeutic strategies for the treatment of asthma can either focus on suppressing the inflammation and bronchoconstriction once they have developed, or can attempt to turn off the aberrant hypersensitivity reaction before it causes airway inflammation and bronchoconstriction.