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

Abstract

Unilateral ventriculocordectomy (VeC) is frequently performed, yet objective studies in horses with naturally occurring recurrent laryngeal neuropathy (RLN) are few. To evaluate respiratory noise and exercising overground endoscopy in horses with grade B and C laryngeal function, before and after unilateral laser VeC. Prospective study in clinically affected client-owned horses. 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 6-8weeks 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. 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. The study sample size was small and multiple dynamic abnormalities made sound analysis challenging. 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.