Feline asthma is a chronic inflammatory disease in which the lower airways constrict too readily in response to stimuli that would not affect normal airways. The resulting clinical signs typically include paroxysmal wheezing, dyspnea, and coughing.

Clinical signs. Dyspnea and coughing are the most frequent signs of feline asthma. Signs typically occur paroxysmally but can be chronic. Signs may be mild or severe and sometimes life-threatening. Owners may mistake coughing for vomiting or gagging. On physical examination, harsh lung sounds, crackles or wheezes are commonly auscultable, and prolongation of expiration may be noted. Increased tracheal sensitivity is frequently present. Some cats will be normal at rest, but auscultation abnormalities can be detected after coughing. Other causes of coughing/wheezing need to be ruled out. These include: congestive heart failure, heartworms, lung parasites, neoplasia, foreign bodies, bronchial infection and pneumonia. The role of Mycoplasma spp. in feline bronchial disease remains uncertain.

Thoracic radiographs. Radiographic changes may be minimal, although there can be accentuated interstitial markings, peribronchial thickenings ("tramlines" and "donuts"), air trapping (hyperlucent lung fields, flattened diaphragm, barrel-chested appearance), right middle lung lobe collapse or patchy alveolar densities (due to mucus plugging of airways and atelectasis).

Cytology. Airway cytology samples can be obtained by trans-tracheal wash or bronchiolar-lavage techniques. While healthy cats often have some eosinophils in the airways, large numbers of these cells may be abnormal, and may indicate allergic or parasitic airway disease. Most cats with bronchitis tend to have large numbers of neutrophils in the airways.

According to Dr. Philip Padrid, the following classification scheme offers a guide to medical therapy of asthma:

• Mild asthma. Symptoms are not present every day. Signs are mild enough to not affect cat's quality of life. Between episodes, appetite and activity are normal.
• Moderate asthma. Signs occur every day. The cat may have mild increased breathing rate or frequency, and there may be a daily cough. The cat is otherwise okay, with normal appetite and some play activity.
• Severe asthma. Signs are present when the cat is at rest. There is significant difficulty breathing. Appetite and activity are usually affected.