Dynamic obstructions of the equine upper respiratory tract. Part 2: comparison of endoscopic findings at rest and during high-speed treadmill exercise of 600 Thoroughbred racehorses.
Authors: Lane J G, Bladon B, Little D R M, Naylor J R J, Franklin S H
Journal: Equine veterinary journal
Summary
# Editorial Summary Diagnosing dynamic upper respiratory tract obstructions in racehorses from resting endoscopy alone is dangerously unreliable, as demonstrated by Lane and colleagues' comparison of endoscopic findings at rest versus high-speed treadmill exercise in 600 Thoroughbreds. Resting endoscopy showed critically poor sensitivity (0.15) for detecting dorsal displacement of the soft palate and palatal instability, with a 35% misdiagnosis rate even when combined with owner-reported respiratory noise. Laryngeal function grading at rest also proved inconsistent: whilst most horses with grade 4/5 dysfunction showed dynamic collapse under exercise, approximately one in five with severe resting scores maintained normal abduction at speed, and conversely, 7% of horses with normal resting grades (1–2) demonstrated collapse only when exerted. The diagnostic accuracy improved substantially to 80% sensitivity when practitioners incorporated clinical history (inspiratory noise), physical examination findings (intrinsic muscle atrophy), and exercise endoscopy together, highlighting the critical importance of dynamic assessment for sound surgical decision-making and pre-purchase evaluations. This evidence should shift practice away from relying on static endoscopic examination in isolation, particularly for high-value racehorses where performance implications are significant.
Read the full abstract on PubMed
Practical Takeaways
- •Do not rely on resting endoscopy alone when assessing racehorses for upper airway obstruction or making pre-sale decisions—dynamic exercise testing is essential for accurate diagnosis
- •Combine resting endoscopy findings with clinical history (inspiratory noise) and palpation for muscle atrophy to significantly improve diagnostic accuracy
- •Understand that laryngeal function at rest is a poor predictor of performance; horses can compensate during exercise despite poor resting appearance, and vice versa
Key Findings
- •Resting endoscopy showed low sensitivity (0.15) for diagnosing DDSP and palatal instability in 600 Thoroughbred racehorses
- •Combined resting endoscopy and owner-reported noises still resulted in 35% misdiagnosis rate for dynamic airway obstructions
- •Diagnostic sensitivity improved to 80% when clinical history of inspiratory noise and palpable intrinsic muscle atrophy were included alongside endoscopy
- •19% of horses with severe laryngeal dysfunction (grade 4/5) maintained full abduction during high-speed treadmill exercise, while 7% with normal resting laryngeal function showed dynamic collapse under exertion