Relationships between equine airway reactivity measured by flowmetric plethysmography and specific indicators of airway inflammation in horses with suspected inflammatory airway disease.

Authors: Wichtel M, Gomez D, Burton S, Wichtel J, Hoffman A

Journal: Equine veterinary journal

DOI: 10.1111/evj.12482 PubMed: 26174367Log in to save

Summary

# Editorial Summary Inflammatory airway disease (IAD) in horses remains diagnostically challenging, particularly in young racehorses presenting with poor performance or cough, because clinicians lack consensus on which diagnostic tools best reflect underlying pathology. Wichtel and colleagues investigated 45 predominantly young Standardbred racehorses using three complementary approaches: flowmetric plethysmography with histamine bronchoprovocation (to measure airway hyperreactivity via PC35 threshold), bronchoalveolar lavage (BAL) cytology (to assess inflammatory cell populations), and endoscopic/tracheal evaluation. Critically, the study found no significant correlation between histamine reactivity and BAL cell counts, meaning these two diagnostic modalities do not validate each other—53% of horses demonstrated airway hyperreactivity whilst only 27% showed abnormal BAL cytology, yet 39% exhibited both abnormalities and 33% displayed one or the other. For practitioners, this lack of concordance indicates that relying solely on BAL cytology risks missing IAD cases in performance horses, since approximately one-third of diagnosed horses would have been missed if only inflammatory cell counts had been evaluated; incorporating reactivity testing via plethysmography appears essential for comprehensive diagnosis in this population.

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Practical Takeaways

•Use both flowmetric plethysmography with histamine bronchoprovocation and BAL cytology for IAD diagnosis in young racehorses with poor performance or cough, as neither test alone reliably identifies all affected horses
•Relying solely on BAL cytology will underdiagnose approximately 33% of cases with airway hyperreactivity; incorporate airway reactivity testing to improve diagnostic sensitivity
•Understand that abnormal airway reactivity and inflammatory cytology represent distinct pathological processes in IAD and may require different management approaches

Key Findings

•No significant correlation found between histamine response (PC35) and bronchoalveolar lavage cytology cell populations in horses with suspected IAD
•53% of horses (24/45) demonstrated airway hyperreactivity when defined as ≥35% increase in flow at histamine concentration <6 mg/ml
•73% of horses (33/45) were diagnosed with IAD based on abnormal BAL cytology and/or AHR, with only 39% (13/33) showing both findings
•Airway reactivity and BAL cytology lack concordance, suggesting these tests measure different aspects of IAD pathology

Conditions Studied

inflammatory airway disease (iad)airway hyperreactivity (ahr)unexplained poor performancechronic cough

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Relationships between equine airway reactivity measured by&#xa0;flowmetric plethysmography and specific indicators of airway inflammation in horses with suspected inflammatory airway disease.