Overground endoscopic findings and respiratory sound analysis in horses with recurrent laryngeal neuropathy after unilateral laser ventriculocordectomy.

Abstract

BACKGROUND: Unilateral ventriculocordectomy (VeC) is frequently performed, yet objective studies in horses with naturally occurring recurrent laryngeal neuropathy (RLN) are few. OBJECTIVES: To evaluate respiratory noise and exercising overground endoscopy in horses with grade B and C laryngeal function, before and after unilateral laser VeC. STUDY DESIGN: Prospective study in clinically affected client-owned horses. METHODS: Exercising endoscopy was performed and concurrent respiratory noise was recorded. A left-sided laser VeC was performed under standing sedation. Owners were asked to present the horse for re-examination 6-8 weeks post-operatively when exercising endoscopy and sound recordings were repeated. Exercising endoscopic findings were recorded, including the degree of arytenoid stability. Quantitative measurement of left-to-right quotient angle ratio (LRQ) and rima glottidis area ratio (RGA) were performed pre- and post-operatively. Sound analysis was performed, and measurements of the energy change in F1, F2 and F3 formants between pre- and post-operative recordings were made and statistically analysed. RESULTS: Three grade B and seven grade C horses were included; 6/7grade C horses preoperatively had bilateral vocal fold collapse (VFC) and 5/7 had mild right-sided medial deviation of the ary-epiglottic fold (MDAF). Right VFC and MDAF was still present in these horses post-operatively; grade B horses had no other endoscopic dynamic abnormalities post-operatively. Sound analysis showed significant reduction in energy in formant F2 (P = 0.05) after surgery. MAIN LIMITATIONS: The study sample size was small and multiple dynamic abnormalities made sound analysis challenging. CONCLUSIONS: RLN-affected horses have reduction in sound levels in F2 after unilateral laser VeC. Continuing noise may be caused by other ongoing forms of dynamic obstruction in grade C horses. Unilateral VeC is useful for grade B horses based on endoscopic images. In grade C horses, bilateral VeC, right ary-epiglottic fold resection ± laryngoplasty might be a better option than unilateral VeC alone. The Summary is available in Portuguese - see Supporting Information.