Restoration of Recurrent-Laryngeal-Nerve Function after Injury in a Rat Model

Abstract

Objectives:

Recurrent laryngeal nerve (RLN) injury occurs in 4-10% of thyroid surgeries. Spontaneous RLN regeneration takes months and is often incomplete. Lithium promotes neuronal growth in vitro. We developed methods to objectively detect vocal-fold impairment in the rat and tested whether systemic lithium enhances recovery after RLN injury.

Methods:

The right RLN was crushed in eight adult rats, and osmotic pumps releasing either lithium or water were implanted. Eight sham-operated animals were also implanted with either lithium or water pumps. Vocal-fold motion was captured by microsuspension laryngoscopy and was measured quantitatively by image analysis at the time of surgery and at one and four weeks. Vocalizations, breathing patterns, and laryngeal electromyography were assessed at four weeks.

Results:

Cessation of unilateral vocal-fold motion was observed simultaneously with every RLN crush. One week after surgery, 50% of “Crush/Water” animals exhibited full vocal-fold motion, compared to 75% of “Crush/Lithium” and 100% of the sham-operated animals. In animals with unilateral vocal-fold immobility, the quantitative analysis also revealed a subtle decrease of vocal-fold movement on the non-operated side. At four weeks after surgery, vocalizations, breathing patterns, vocal-fold motion, and electromyograms were indistinguishable among all groups. Lithium-treated animals weighed 5% less than water-treated controls.

Conclusions:

Quantitative endoscopy is a sensitive and efficient tool for detecting vocal-fold impairment in rats. While our results might suggest enhanced recovery in lithium treated animals, all animals showed a rapid return of vocal-fold motion. Perhaps more severe nerve injury is necessary to uncover an effect of lithium on nerve regeneration.