Utilizing novel recurrent laryngeal motor nerve conduction studies to characterize the aging larynx: A pilot study

Abstract

Abstract Objectives Age‐related changes to the larynx are associated with dysphonia and contribute to reduced quality of life. This study utilizes recurrent laryngeal motor nerve conduction studies (rlMNCS) to determine if neurophysiologic changes occur in the aging larynx using an aging rat model. Study Design Animal study. Methods In vivo rlMNCS were performed in 10 young hemi‐larynges (3–4 months) and 10 aged hemi‐larynges (18–19 months) rats (Fischer 344 × Brown Norway F344BN). Recording electrodes were placed into the thyroarytenoid (TA) muscle through direct laryngoscopy. Recurrent laryngeal nerves (RLNs) were directly stimulated with bipolar electrodes. Compound motor action potentials (CMAPs) were obtained. RLN cross‐sections were stained with toluidine blue. Axon count, myelination, and g‐ratio were quantified utilizing AxonDeepSeg analysis software. Results rlMNCS were successfully obtained in all animals. Mean CMAP amplitude and negative durations in young rats were 3.58 ± 2.20 mV and 0.93 ± 0.14 mS (mean dif: 0.17; 95% CI: −2.21 to 2.54), respectively, and 3.74 ± 2.81 mV and 0.98 ± 0.11 mS (mean dif: 0.050; 95% CI: −0.07 to 0.17). No significant differences in onset latency or negative area were observed. Mean axon count in young rats (176 ± 35) was comparable to that in old rats (173 ± 31). Myelin thickness and g‐ratio did not differ between groups. Conclusions There were no statistically significant differences in RLN conduction or axon histology between young and aged rats in this pilot study. This work provides a basis for future, adequately powered studies, and may lead to a tractable animal model to study the aging larynx. Level of Evidence 5.

Keywords

• age‐related vocal atrophy
• aging voice
• compound motor action potential
• motor nerve conduction studies
• Neurolaryngology
• recurrent laryngeal nerve