Differentiating Feline Inflammatory Airway Disease

Inflammatory airway disease is a common respiratory condition in young to middle-aged cats and has historically been divided into feline asthma and chronic bronchitis. These respiratory diseases have overlapping clinical and radiographic features, and a bronchoalveolar lavage sample is needed to differentiate between them.  

This study evaluated the clinical and radiographic features of 49 cats with inflammatory airway disease. Cats were categorized as having eosinophilic (>20% eosinophils with <14% neutrophils, or >50% eosinophils), neutrophilic (<20% eosinophils with >14% neutrophils), or mixed airway inflammation (20%-50% eosinophils with >14% neutrophils). Group comparisons included type and duration of clinical signs, signalment, CBC results, and thoracic radiograph findings. The goal of the study was to determine factors that may aid in differentiating between inflammatory airway syndromes in cats.  

Cats in the eosinophilic inflammation group tended to be younger (4.4 ± 3.3 years) as compared with cats in the neutrophilic (8 ± 5.6 years) and mixed (7.5 ± 4 years) inflammation groups. Cough was the most common presenting clinical sign (84%) in all cats, and duration of clinical signs, CBC results, and thoracic radiograph findings did not differ among groups. Sneezing (or nasal discharge) was the second most common clinical sign (39%) in all cats; however, this was not found to be correlated with any of the inflammatory airway disease groups. This finding is in contrast with a recent study in which cats with chronic bronchitis were more likely to have nasal discharge than cats with feline asthma.¹ A correlation between nasal discharge and type of airway inflammation was not found in this study. 

Although few cats in the study had peripheral eosinophilia (>1100 eosinophils/µL) on CBC, 5 of 6 cats with peripheral eosinophilia had eosinophilic airway inflammation, and 1 of 6 had mixed inflammation. The predominant pulmonary pattern was bronchial (79%), followed by interstitial (51%) and alveolar (38%). Only 9% of cats had normal thoracic radiographs. These findings correlate with previous studies evaluating radiographic features of cats with airway inflammation.²

Key pearls to put into practice:

Feline inflammatory airway disease commonly results in cough, tachypnea, and, occasionally, nasal discharge. Differentiating among neutrophilic, eosinophilic, and mixed airway inflammation with noninvasive diagnostics (eg, CBC, thoracic radiography) can be a challenge.

Infectious diseases that can mimic feline asthma and chronic bronchitis based on clinical features and radiographic findings should be considered. It is also important to consider noninvasive diagnostics for pulmonary parasites, feline heartworm disease, and fungal disease (eg, Histoplasma capsulatum) based on geographic location.

Although clinical signs and diagnostic results may overlap, treatment for inflammatory airway disease is similar, with anti-inflammatory doses of oral prednisolone being the mainstay of treatment. Transition to inhaled fluticasone should be considered in select cases.