Experimental crush of the equine recurrent laryngeal nerve: a study of normal and aberrant reinnervation.

The research investigates the process of reinnervation in healthy ponies after their recurrent laryngeal nerve is damaged, through the use of endoscopic, electromyographic, and microscopic techniques. The authors examine the recovery of vocal fold function and find evidence of both normal and aberrant reinnervation.

Methodology

• The researchers damaged the recurrent laryngeal nerve in 12 healthy ponies by crushing it unilaterally in the midcervical area.
• Postoperative effects were observed and all the ponies demonstrated paralysis of the larynx on the side that was operated on.
• Observation and evaluation were done over periods of time, ranging from 2.5 to 8 months, to determine the reinnervation process and any changes in vocal fold function.

Findings

• Eight ponies showed some recovery of vocal fold movement post-surgery, although the movements were often abnormal and included trembling and asynchronism.
• Only two ponies had a complete return of normal vocal fold function.
• Reinnervation was explicitly identified as the cause of return of function. This was determined through an electromyographic examination of the laryngeal muscles and microscopic evaluation of these muscles and the recurrent laryngeal nerves.
• They observed regenerative activity in the nerves and evidence of fiber-type grouping in the muscles.
• In three ponies, the researchers noticed aberrant or unusual reinnervation, which showed symptoms like adductor or abductor muscles discharging during an inappropriate phase of the respiratory cycle.

Comparison with spontaneous subclinical laryngeal paralysis

• The researchers compared the endoscopic abnormalities observed in the ponies with those observed in horses suffering from spontaneous subclinical laryngeal paralysis.
• However, they were skeptical about the likelihood of the abnormal findings in this latter group of horses being due to aberrant reinnervation.

Conclusion

• The study brings to light the occurrence of both normal and aberrant reinnervation post-damage to the recurrent laryngeal nerve in healthy ponies.
• More precisely, the abnormal reinnervation might contribute to the dysfunction observed in the horses’ vocal fold function post-surgery.
• Thus, this study creates a foundation for further research into the effects of reinnervation on vocal fold function and potential treatments to improve recovery.