Associations between clinical signs, endoscopic and cytological findings in equine bronchoalveolar lavage samples

Background: Endoscopy, including tracheal mucus score (TMS) and bronchoalveolar lavage (BAL) fluid cytology, is commonly employed in the diagnosis of equine asthma (EA). Large-scale studies comparing clinical signs, TMS and BAL cytology are warranted. Objectives: To investigate associations between clinical signs of EA, tracheal mucus score and BAL cytology. Study Design: Cross-sectional study. Methods: Data were collected from 604 horses, each with a single BAL cytology sample evaluated by the laboratory service at the Large Animal Teaching Hospital in Denmark. Additional information was obtained through owner questionnaire and reports from the veterinarian performing endoscopy and BAL procedures. Results: The TMS increased significantly with EA severity, BAL neutrophilia and owner-reported coughing, but not with BAL mastocytosis. Owner-reported coughing was associated with a higher percentage of BAL neutrophils but not with an increased percentage of BAL mast cells. Poor performance was not correlated to BAL neutrophils, mast cells or TMS. The percentage of BAL fluid retrieved was lower in the SEA group compared to the MEA and non-asthmatic groups. Main Limitations: BAL sampling was performed by multiple veterinarians; samples were shipped with up to a 24-h delay in processing, and seasonal effects were not accounted for. Conclusion: This large-scale study identified a correlation between TMS and increasing severity of lower airway inflammation, confirming TMS as a reliable diagnostic factor for EA. Owner-reported coughing was associated with both TMS and BAL neutrophilia. However, poor performance in the absence of coughing was not found to be a reliable indicator of EA.