Abstract
Background:
Equine asthma is a common, non-infectious, chronic lung disease that affects up to 80% of the horse population. Diagnostic guidelines rely on history, clinical presentation, and neutrophil count in bronchoalveolar lavage fluid. However, strict phenotyping and identification of subclinical asthmatic horses can be challenging. The aim of this study was to describe the equine asthma phenotypes (mild, moderate, and severe asthma) in a clinical population and identify the variables and examination steps with best discriminative potential. A standardised examination protocol was used, which included clinical examinations, blood work, airway endoscopy with bronchoalveolar lavage fluid analysis, arterial blood gas analysis and radiography.
Results:
Out of 26 horses, four were diagnosed with mild (subclinical), seven with moderate, and seven with severe asthma. Eight horses served as controls with no evidence of respiratory disease. Cough with history of coughing was the strongest clinical variable in phenotype differentiation. All horses with mild asthma were distinguishable from healthy individuals by mast cell counts in bronchoalveolar lavage cytology only. Moderate and severe asthmatic horses were characterised by clinical symptoms and neutrophil counts. Regardless of data subsets used in algorithmic evaluation of classification trees, a differentiation of three phenotypes without neutrophil and mast cell counts in bronchoalveolar lavage cytology is not sufficient for clinical diagnostics. Factor analysis revealed an increasing clinical variability with disease severity and an overlapping of clinical presentations between the phenotypes.
Conclusions:
Equine asthma phenotypes are clinically variable with overlapping symptom severities. History of coughing and bronchoalveolar lavage cytology are the strongest discriminant parameters. Mild asthma is differentiated by bronchoalveolar lavage cytology only. The results indicate that medical history, clinical examination and bronchoalveolar lavage cytology are indispensable steps to diagnose equine asthma and that a comparably exact diagnosis cannot be achieved by relying on alternative examinations or surrogate variables. An absence of single symptoms does not necessarily indicate an absence of advanced disease, while the presence of symptoms indicates disease severity. Diagnosing equine asthma should rely on medical history, clinical examination, and endoscopy including bronchoalveolar lavage cytology. Screenings of inconspicuous horses with bronchoalveolar lavage can aid in diagnosing subclinical affected animals.