Diagnostic Approach to the Coughing Cat Algorithm

The coughing cat presents a clinical challenge. Coughing is a nonspecific clinical sign, and differentials include infectious conditions such as viral, bacterial, and parasitic disease; neoplasia; and noninfectious feline lower airway disease (FLAD), which includes classic feline asthma, bronchiectasis, and chronic bronchitis. Cardiogenic disease rarely causes coughing as a primary clinical sign in cats but should remain a differential.

Initial assessment of patient signalment, history, and physical examination findings should consider patient lifestyle risk factors; the character of the cough; the presence of pyrexia; respiratory rate and effort; and 4-quadrant lung auscultation for abnormal sounds such as crackles, wheezes, or rales. If the patient is in respiratory distress, all other diagnostics must wait until the patient has been stabilized. In emergent cases, or those in which cost constrains a full diagnostic workup, therapeutic drug trials may be necessary.

In all other cases, thoracic radiography is the next essential step in the diagnostic workup of a coughing cat. Assessment of lung pattern and distribution of pattern can quickly narrow the differential list. Cats with FLAD often have lung hyperinflation and a diffuse bronchial or bronchointerstitial pattern, resulting in a classic “donut” or “tram line” effect due to bronchial wall thickening. Radiographically, parasitic disease may appear similar. Cats with pneumonia may be more likely to present with an interstitial to alveolar lung pattern that is most likely to affect the ventral lung fields.

Blood analysis is useful to evaluate a patient’s overall health status, and heartworm antibody and antigen testing should be performed as part of this assessment. Approximately 14% to 40% of cats with FLAD may have  peripheral eosinophilia on CBC.^1,2 Eosinophilia on CBC should increase suspicion for FLAD or parasitic causes of cough. A neutrophilic inflammatory leukogram is more commonly encountered in cases of infection.³

If the patient is clinically stable, the next diagnostic step after obtaining an initial radiographic assessment and establishing overall health status is lower airway sampling. Blind bronchoalveolar lavage (BAL) techniques are well described in the literature, are readily accessible, and show similar sample quality to that of bronchoscopically guided techniques.⁴ Fluid sample evaluation includes cell count, cytology, and culture. Cats in significant respiratory distress are not candidates for BAL. Evaluation of NT-proBNP (N-terminal pro–B-type natriuretic peptide) level at the start of the diagnostic workup for a coughing cat can be useful in decreasing clinical suspicion for cardiogenic disease as a differential and establishing stability for undergoing anesthesia for BAL.

Developing a streamlined but comprehensive diagnostic approach that considers patient clinical history, physical examination findings, radiographic evaluation, blood analysis, parasite testing results, and lower airway sampling is essential to obtaining an accurate diagnosis (Box 1) and informing an effective therapeutic plan.