Functional Phenotype and its Correlation with Therapeutic Response and Inflammatory Type of Bronchoalveolar Lavage Fluid in Feline Lower Airway Disease

Abstract

BackgroundCurrently, functional assessment to monitor therapeutic response in feline lower airway disease (FLAD) has limited application.ObjectivesTo evaluate if expiratory indices derived from pseudo‐tidal breathing flow‐volume loop (pTBFVL) representing lower airway obstruction would decrease after clinical improvement and to investigate the correlation between functional phenotype and inflammatory cell type in bronchoalveolar lavage (BAL) fluid.AnimalsNineteen client‐owned cats with FLAD.MethodsProspective observational study. Functional assessment with pTBFVL indices (eg, peak to mid‐expiratory flow; PEF/EF50) and conventional barometric whole body plethysmography (BWBP) parameters (eg, enhanced pause) was carried out before receiving treatment. BAL was performed to analyze inflammatory cell types. Signs were assessed by scoring. The cats were treated with glucocorticoids daily and functional testing was repeated.ResultsLoop indices PEF/EF50 and PEF/EF25 were significantly decreased after treatment (P < .001). Conventional BWBP parameters were not significantly different before and after treatment. Cats with PEF/EF50 > 1.51 before treatment had a significantly higher granulocyte (eosinophil plus neutrophil) percentage in BAL fluid (P = .014). Granulocyte percentage in BAL fluid was strongly correlated with PEF/EF25 (P = .001, r s = 0.74) and moderately correlated with PEF/EF50 (P = .022, r s = 0.57), whereas eosinophil or neutrophil percentage alone had no significant correlation with functional parameters.Conclusions and Clinical ImportanceFunctional parameters including PEF/EF50 and PEF/EF25 can be used for monitoring therapeutic response. The presence of airflow limitation during mid‐ to late expiration is affected by the overall extent of granulocyte infiltration.

Clinical features and radiographic findings in cats with eosinophilic, neutrophilic, and mixed airway inflammation (2011‐2018)

“…Airway eosinophilia was the most common IAD (47%) in our group of cats, which is similar to recent studies, 8,11,13,15,20 but other, primarily older, publications 1‐3 have reported eosinophilic inflammation in a smaller proportion (24%‐32%) of cats evaluated. This difference might suggest an increasing trend toward eosinophilic disease in cats, which is interesting considering that allergic and asthmatic diseases have been increasing in people 21 .…”

“…Neutrophilia predominates in the allergic disease process in horses partially because of IL‐4‐mediated release of neutrophilic chemotactic factors, 31 and the severity of disease correlates to some extent with the severity of airway neutrophilia 32 . The cytokine milieu in the respiratory tract of cats with naturally occurring airway disease has not been evaluated, but 1 study did associate the magnitude of airway inflammation with the clinical and radiographic severity of disease, 3 and airway responsiveness has been correlated with the severity of airway inflammation 8,15 …”

“…Cats were categorized as having eosinophilic, mixed, or neutrophilic inflammation based on BAL fluid differential cytology. Previous reports have used eosinophil percentages of >17 to 20 8,15‐18 to define eosinophilic inflammation, and neutrophil percentage exceeding the reference range to describe noneosinophilic or neutrophilic inflammation. Other studies define inflammation based on the prominent cell type.…”

“…Similar to some forms of the syndrome in humans, asthma in cats has been suggested to result from exposure to allergens, and a disease syndrome typified by eosinophilic airway inflammation can be created experimentally by allergen or antigen challenge 2‐4,7 . In contrast, chronic bronchitis in cats is defined by the presence of cough, and bronchoconstriction is not part of the clinical picture 2,8 . Chronic bronchitis in cats has been defined similarly to the disease in dogs 9 with development of nonseptic suppurative airway inflammation in response to an unknown insult.…”

“…Previous studies evaluating clinical findings in cats with naturally occurring disease have failed to identify clinically relevant differences between cats with asthma and those with chronic bronchitis, with the exception of some investigators noting younger age in cats with airway eosinophilia 1,5,8,13,15 . The purpose of our retrospective study was to investigate clinical variables that could aid in differentiation between inflammatory airway syndromes in a large group of cats with naturally occurring disease in which standardized diagnostic testing, including bronchoscopic bronchoalveolar lavage (BAL), had been performed.…”