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