By Larry Greenemeier
(Click here for the original article)
When Google CEO Larry Page blogged about his struggles speaking and, at times, breathing last week on his Google+ page he spotlighted a rare condition, bilateral vocal cord paralysis, which leaves sufferers short of breath and with few viable treatment options. This is likely to change in coming years. Page has deep pockets and has promised to fund research into the disorder via the Voice Health Institute. In the meantime scientists are experimenting with electrical stimulation technologies to enhance existing voice therapy as well as surgical treatments.
Vocal cord paralysis, or, more accurately, vocal fold paralysis (they're not really "cords") occurs when the nerve impulses to the larynx, or voice box, are interrupted. This can lead to paralysis of the vocal fold muscles on either side of the throat, impeding speech and even the ability to breathe. Because these folds protect a person's airway from being choked by food, drink and saliva, bilateral paralysis--a rare variety that affects vocal folds on both sides of the larynx--can be life threatening.
Depending on the severity of the paralysis, patients can be treated using voice therapy, injections or surgery. In more extreme cases a patient might need a tracheotomy in order to continue breathing. New, experimental approaches to treating the condition seek to use electrical stimulation to move the vocal folds.
Electrical vocal fold stimulation faces two main challenges--it must stimulate the correct muscles, and has to achieve the right motion and correct vocalization, says Alexander Leonessa, an associate mechanical engineering professor at Virginia Polytechnic Institute and State University's Center for Autonomous Systems. Leonessa leads a team of researchers who for the past few years have been experimenting with stimulators that, when placed on the neck, would generate electrical signals to activate the nerves governing vocal fold movement.
His latest approach involves designing a microcoil that could be implanted or injected into a patient's neck, near the muscle that needs to be stimulated. That coil would interact with a larger coil placed around the neck--perhaps on a necklace--to generate a variable magnetic field that could generate the necessary electric stimulation. Leonessa's team has used this approach in the lab to stimulate different levels of contraction in muscle removed from a mouse leg. This will help the researchers pinpoint specific muscles for stimulation and even stiffen the vocal fold to the necessary amounts to produce different sounds. The researchers are planning animal testing of their stimulator by the end of the year.
To learn more about vocal fold paralysis and its treatment, Scientific American spoke with Christy Ludlow, professor of communication sciences and disorders and director of James Madison University's Laboratory on Neural Bases of Communication and Swallowing.
[An edited transcript of the interview follows.]
What is vocal fold paralysis?
It means that the vocal folds are not moving. Normally we open our vocal folds to breathe and close them to speak or to swallow. When a vocal fold is paralyzed, it's somewhat unpredictable what position it's going to be in. A fold can be stuck in what's known as the paramedian position, halfway between open and closed. When one side is paralyzed the person can have a breathy voice, as the condition typically affects the ability to close the larynx, which is important for speaking and swallowing.
If both vocal folds are in the paramedian position, you'll have a weak voice, some reduction in your breathing capacity and some swallowing difficulties. If one fold is paralyzed to the side and the other is paralyzed in the center, then you'll have a weak voice as well as breathing problems. If both vocal folds are paralyzed and sit [closed] in the midline [of the throat], such a closure can create a critical breathing problem, and that's when someone may need a tracheotomy--to create an airway below the larynx--in order to be able to breathe. Often, to treat the breathing problem you have to sacrifice [a patient's ability to speak].
What typically causes vocal fold paralysis?
There are different muscles that open and close the vocal folds. Both sets of muscles are controlled by what's known as the recurrent laryngeal nerves. The left recurrent nerve is much longer than the right--it goes down and wraps around the aorta of the heart and comes back up along the tracheal esophageal groove. Because it is a longer nerve, the left side is more likely to be injured, for example, during heart surgery or a thyroidectomy--where the thyroid gland is removed due to cancer--or to be affected by aging or viral infections.
What type of viral infection might damage the vocal folds?
Although not common, a virus can be absorbed into the mucosa lining the upper respiratory area in the trachea, particularly in the larynx. The virus can be transported from the mucosa back through the nerve, causing inflammation and damage to the nerve. We don't really understand which viruses do this; there's a lot more research needed.
Could someone have genetic disposition toward vocal fold paralysis?
There can be genetic bases for familial recurrent nerve palsy, which can start in young children or is not noticed until middle age. In some cases the gene producing a motor protein that moves molecules from the end of the nerve back up to the nucleus may be mutated. There's not the normal transport of molecules to keep the nerve healthy. This type of nerve palsy usually doesn't occur until people reach their 40s or 50s, but in some families where this trait is dominant it can affect very young children and even infants who have vocal fold palsy at birth. In those cases the infant often must have a tracheotomy to open up their windpipe.
What is the typical course of treatment?
If the paralysis is the result of a surgical procedure that injures the nerve, the patient should be seen by an otolaryngologist, who does surgery on the vocal folds. The otolaryngologist will decide what is the best course for treatment. If the patient doesn't have any problems swallowing, the patient may use voice therapy with a speech pathologist to learn to improve their voice while the nerve regenerates. This is done to keep the patient from developing some sort of abnormal compensation as the nerve heals.
If the person has severe swallowing problems, an otolaryngologist may inject substances into the vocal fold. This will bulk up the fold that's paralyzed and move it more to the center [of the throat]. That will usually last six months or so, just to get the patient through the time while the nerve is growing back. If the nerve doesn't grow back, the otolaryngologist may do a procedure called a thyroplasty, where they put a wedge into the paralyzed side to move the fold permanently more towards the center of the throat. That helps with the voice and swallowing. It may not make it normal but it will significantly improve. Another approach is to suture a fold towards the center of the larynx or to suture another nerve to the end of the damaged nerve, although that's done less frequently than a thyroplasty.
What new technologies in development might better help people suffering from vocal fold paralysis?
David Zealear at Vanderbilt University has been working for a couple of decades on electrical stimulators that can be implanted into the muscles in the back of the larynx for people who have bilateral vocal fold paralysis to help them breathe. [Zealear and his team are developing an implantable laryngeal pacemaker that could restore normal breathing through the mouth without injuring the vocal folds, a project unrelated to Leonessa's electrical stimulation work.] The pacemaker can be programmed so that the vocal folds open for each breathing cycle. If there's damage to the muscle, however, a stimulator would not work.
If you don't have an intermittent stimulator like what Zealear is working on, there is a permanent surgical procedure where you pull one of the vocal folds to one side to provide an airway. This, of course, would affect your ability to speak.
How common is vocal fold paralysis?
Left-side paralysis is more common than paralysis on the right side, but it's very rare that someone would have paralysis on both sides. The last I heard was 200 new cases per year of bilateral vocal fold paralysis.
What are the chances that a person will recover from this condition?
Often, when there's an injury to the recurrent laryngeal nerve, it will spontaneously "re-enervate," meaning the nerves will grow back. That depends upon how high up [the throat] the lesion is. If the lesion is up to the point where it emits from the skull, then you're going to have a very long pathway for that nerve to grow back. In some cases the nerve can also grow back to the wrong muscle. If the injury is close to where the nerve goes into the larynx, then your chances of re-enervation are pretty high. Usually, within three months you'll see some signs of re-enervation. Within nine to 12 months final re-enervation can be completed.