Neurolaryngology study group - Reanimation of the Posterior Cricoarytenoid Muscle: Reinnervate or electrically stimulate?
The neurolaryngology study section had an interesting presentation on the treatment of bilateral recurrent laryngeal nerve injury (paralysis/paresis/synkinesis) chaired by Lucian Sulica and Stacy Halum. Speaker David Zealear, Ph.D. from Vanderbilt began by mentioning iatrogenic thyroidectomy as the number one etiology behind bilateral recurrent laryngeal nerve injury. He spoke about three of his research projects for dealing with this injury.
AAO-HNS Meeting at the Washington Convention Center, Washington, DC - September 11, 2012
He started first with a clinical study of 6 patients who had a stimulator implanted into the PCA (posterior cricoarytenoid) muscle with an electrical stimulater. The implant stimulated during inspiration and was off during expiration, allowing the larynx to return to its resting position. He compared the breathing and voice results to a group of patients who had some type and degree of cordotomy.
His main measurement was peak airflow which he reported, “was statistically improved”. I noticed on the data slide that several of the patients had no measurable airflow at all before the procedure - which isn’t to say they had no airflow, but it wasn’t reportedly measurable when I asked him later.
He felt that 5 of the 6 patients had a good result, in that peak airflow improved and additionally voice improved and that both of these parameters were better than in patients with cordotomies. However, voice was still not “normal” and a botulinum toxin injection into the adductor muscles further subjectively improved the voice.
This is an incredibly thought-provoking sturdy, although there are so many variables in the glottic opening in a bilateral nerve injury and so many variables after a cordectomy in terms of the glottic opening and vocal cord mobility (abduction and adduction), that I found the statistical part of the presentation to be not that helpful. There clearly was an effect. It was very beneficial. (I have not found it necessary to use cordotomy in a bilateral recurrent laryngeal nerve injury so I was most interested in the study arm of the group rather than the comparison.)
After this study, in a second report, several canines were given a bilateral paralysis by a complete severing of each RLN with immediate reanastomosis. This produced a dyskinetic adduction during inspiration and a dyspneic dog. He used 2-channel electrodes normally used for deep brain stimulation, leaving them in for 10-21 months in four dogs. This stimulation was not synchronized but rather intermittently opened the office, rather well on the video endoscopies shown. He demonstrated that this asynchronous opening resulted in very adequate ventilation even during active exercise testing. It also did not result in swallowing problems, as the dog could still close the glottis overriding the stimulator. He noted that they implanted the stimulators as close to the median raphe of the posterior cricoarytenoid muscle as possible to avoid bleed-over of the stimulatory signal into the abductor muscles.
The third study that he presented, demonstrated in 2 animals that continuous or intermittent stimulation of a denervated muscle during the recovery period at a “moderate rate” of 10 pulses per second (4 seconds on, 4 seconds off) seemed to lead to more appropriately directed reinnervation than either no electrical stimulation or a higher rate or quantity of stimulation.
In summary, his research suggests that there may be a management pathway for implantable nerve or muscle stimulators to open the vocal cords in patients experiencing a bilateral recurrent laryngeal nerve injury with dyskinetic reinnervation and an inadequate inspiratory airway.
If you are a laryngologist and you're interested in being on the mailing list for neurolaryngology study group you should contact Lucian Sulica.