Definitive diagnosis of feline asthma can be challenging due to clinical features that overlap with various other cardiopulmonary conditions, including chronic bronchitis, heartworm-associated respiratory disease, and pulmonary parasitic disease. Diagnosis can be facilitated through a combination of consistent historical information, clinical signs (ie, cough and/or respiratory distress), physical examination, laboratory data (eg, CBC, serum chemistry profile, fecal flotation and analysis, urinalysis, heartworm antigen and antibody testing), imaging (eg, thoracic radiography, thoracic ultrasonography, CT, bronchoscopy, echocardiography), airway sampling, and additional diagnostic testing (eg, airway cytology) to rule out other causes of eosinophilic airway inflammation.
Physical examination may be normal or may reveal tachypnea, inducible cough on tracheal palpation, and/or abnormalities on thoracic auscultation (eg, increased bronchovesicular sounds, expiratory wheezes). Classic radiographic findings include a diffuse bronchial or bronchointerstitial pattern, hyperinflation due to air trapping, and/or collapse of the right middle lung lobe due to mucus plug obstruction (Figure 1).3,4 Because ≈20% of asthmatic cats have normal thoracic radiographs, asthma should remain on the differential list for any cat with respiratory distress and normal thoracic radiographs.5 In addition, a bronchial or bronchointerstitial pattern is also the predominant pulmonary pattern seen in cats with chronic bronchitis and/or heartworm-associated respiratory disease, making it challenging to differentiate these conditions from asthma via only physical examination and radiography.