A look at airway inflammation in cats

Lee EA, Johnson LR, Johnson EG, Vernau W. Clinical features and radiographic findings in cats with eosinophilic, neutrophilic, and mixed airway inflammation (2011‐2018). J Vet Intern Med. April 2020.

Lower airways disease is the most common cause of chronic cough in cats. It is composed of two syndromes; asthma and chronic bronchitis.  Asthmas consists of increased airway responsiveness and bronchoconstriction, likely as part of an allergic syndrome and potentially responsive to bronchodilators. Chronic bronchitis consists of airway inflammation with less bronchoconstriction. Both diseases present similarly clinically, radiographically, and haematologically. While asthma is characterized by a large number of airway eosinophils, this may also be seen in normal cats. As a result, definitively diagnosing asthma vs chronic bronchitis is difficult. The purpose of this study was to determine if a combination of clinical variables could differentiate these conditions.

This study was designed as a retrospective observational study investigating cats undergoing bronchoscopy with bronchoalveolar lavage (BAL) at a veterinary teaching hospital over a period from 2011 to 2019. Included cats had a negative response to antimicrobials and positive response to corticosteroids, with no evidence of neoplasia, infection, parasite, foreign body, or trauma. BAL samples were required to have >= 300 cells/uL.

Signalment, clinical signs, PE findings, lifestyle, bronchoscopy findings, BAL findings, CBC, fecal, heartworm, and radiographic findings were analyzed. Data was statistically evaluated to look for significant differences between groups based on the pattern of BAL fluid attained.

Ninety-nine cats were included in initial analysis, of which 50 cases were excluded due to diagnosis of pneumonia (26), neoplasia (14), tracheal tear (1), and upper airway obstruction (1). Forty-nine cats were therefore included in final analysis. Median age was 5 years, with 28 neutered males and 21 spayed females.  Of the 40 cats, 23 (47%) has eosinophilic inflammation, 12 (25%) neutrophilic, and 14 (29%) mixed.

Cough was the most common presenting complaint, followed by sneezing or nasal discharge, increased respiratory effort, and wheezing. There was no difference in clinical signs, respiratory rate or respiratory effort between cats with different BAL cytology patterns. Cats with eosinophilic inflammation were significantly younger than cats with neutrophilic or mixed inflammation (4.4 vs 8.0 vs 7.5 years respectively).

The most common radiographic pattern was bronchial, followed by interstitial. No difference was found in radiographic patterns or radiographic severity score. There was no correlation between duration of cough or severity score. While cats with very high peripheral eosinophil counts generally had eosinophilic airway inflammation, most cats with asthma had normal eosinophil counts and there was no significant difference between groups.

This study was somewhat limited by the retrospective nature and long period of time over which analysis occurred (leaving room for changes in both patient characteristics and diagnostic technique). A relatively small sample size was utilized, especially once stratified into individual groups.

This study concluded that there is no significant difference in presenting signs or diagnostic findings between cats with eosinophilic, mixed, or neutrophilic lower airway inflammation, with the exception of age. Despite a statistically significant difference, there is large enough overlap in age ranges to make clinical relevance extremely limited. (MRK)

See also:

Lin CH, Wu HD, Lee JJ, Liu CH. Functional phenotype and its correlation with therapeutic response and inflammatory type of bronchoalveolar lavage fluid in feline lower airway disease. J Vet Intern Med. 2015;29(1): 88-96.