Nasopharyngeal and laryngopharyngeal collapse: intra- and interrater agreement supports novel endoscopic scoring classifications in horses.

Overview

• This study introduces new endoscopic scoring classifications to distinguish between nasopharyngeal collapse (NPC) and laryngopharyngeal collapse (LPC) in horses and evaluates the reliability of these classifications through intra- and interrater agreement analyses.
• The research focuses on improving the understanding and assessment of pharyngeal collapse, a condition affecting airway patency during exercise in horses.

Background and Purpose

• Pharyngeal collapse in horses is linked to respiratory issues and decreased performance, but the exact causes related to airway narrowing—whether due to inspiratory pressure or muscular contraction—are not well understood.
• Traditional classifications treat the pharyngeal region as a whole, despite clear anatomical differences between its rostral (front) and caudal (back) sections.
• This study proposes novel classifications and grading scales to categorize two distinct collapse types:
  • Nasopharyngeal collapse (NPC): Collapse occurring rostral to the epiglottis tip, graded 0–4 based on severity.
  • Laryngopharyngeal collapse (LPC): Collapse occurring caudal to the epiglottis tip, graded 0–3.

Methods

• Retrospective analysis of clinical records from 99 barrel racing horses in Southern Alberta, diagnosed with pharyngeal collapse between 2015 and 2025.
• Horses referred for respiratory issues or poor performance underwent overground endoscopy during high-speed exercise to capture still images for analysis.
• Two independent raters, blinded and randomized, assessed these images using the newly proposed NPC and LPC classification/grading systems.
• Statistical methods employed:
  • McNemar test for classification agreement (presence or absence of collapse)
  • Weighted kappa (κ) statistic for scoring agreement (grading severity)

Results

• Incidence rates:
  • 64.6% of horses exhibited nasopharyngeal collapse (NPC).
  • 67.6% exhibited laryngopharyngeal collapse (LPC).
  • 32% demonstrated both types of collapse.
• Intrarater Agreement (same rater on repeated assessments):
  • NPC classification: χ2 = 7.0 for rater 1, χ2 = 1.0 for rater 2.
  • LPC classification: χ2 = 2.0 for rater 1, χ2 = 1.6 for rater 2.
  • Scoring agreement:
    • Good to very good for NPC (κ = 0.69 to 0.81), indicating consistent grading within raters.
    • Moderate to good for LPC (κ = 0.56 to 0.80), showing slightly less but acceptable consistency.
• Interrater Agreement (between different raters):
  • NPC classification: χ2 = 4.6 and χ2 = 0.7 for two raters, indicating some variability but general agreement.
  • LPC classification: χ2 = 0.2 and χ2 = 2.0, reflecting lower but still acceptable agreement.

Conclusions and Implications

• The analysis supports the practicality and reliability of distinguishing between NPC and LPC using the proposed endoscopic classifications and grading systems.
• Reliable intra- and interrater agreement indicates that these novel scoring systems can be applied consistently by different clinicians or researchers.
• Recognizing anatomical and functional differences between nasopharyngeal and laryngopharyngeal collapse may help in understanding the mechanisms underlying pharyngeal collapse more precisely.
• This improved understanding has potential clinical benefits, such as targeted diagnosis and treatments to manage respiratory problems and improve performance in affected horses.
• Overall, the research advances equine respiratory diagnostics by promoting standardized and anatomically informed assessment tools.