April 12, 2016 -- Doctors don't usually try to get on your nerves. But they've been doing it more and more in recent years -- eyeing one particular nerve -- in the hopes that it can treat many long-term or life-threatening conditions.
"[VNS] affects our brain circuitry in a profoundly powerful way," says Mark S. George, MD, director of the brain stimulation laboratory at the Medical University of South Carolina. "I think there is going to be a renaissance of vagus nerve stimulation over the next 10 years."
That's Some Nerve
So, what makes the vagus special? It's the major nerve that connects and sends messages back and forth between your brain and many organs. Tucked behind the major vessels on both sides of your neck, it weaves its way from your brain to below your belly. The wandering nerve is actually a fiber bundle that branches off and contains tens of thousands of smaller nerve fibers. Think of it like an electrical cord -- if you cut one open and peek inside, you'll find it filled with many tiny wires.
Every one of the nerves inside the vagus helps your body do something important.
"One of those nerves comes from my stomach, and tells me when I'm full or not. Another comes from the heart and tells me if I have pain. Another comes from my lungs and tells me if I'm short of breath," George explains.
"Not only can you select which fibers you want to target with VNS, you can also control which way you want the information to go and your effect," he says.
It Started With Seizures
The FDA approved the first vagal nerve stimulation device just over 2 decades ago for epilepsy. The pacemaker-like device delivers pulses of electricity to help keep seizures at bay. About half of people who have this treatment see their seizures drop by 50%.
Soon after approval, people who had the Cyberonics VNS therapy system implanted started reporting better, happier moods. That prompted researchers to ask if stimulating the vagus could affect one's mental health.
In 2005, the FDA approved the same system to help against treatment-resistant depression in adults.
George says for those patients that respond, the treatment works very well. But they have no way to predict who may respond. And outpatient surgery is needed to implant the device under the skin in the left side of the chest for both epilepsy and depression. That runs upwards of $30,000.
The costs and the surgery have kept the treatment from becoming widely adopted, George says.
"The use of VNS for depression would greatly increase if the cost were less and if we could better predict who will benefit before they had surgery," he says.
A device the FDA approved last year, the Maestro Rechargeable System, tackles something entirely unexpected: obesity. You might say scientists stumbled onto this use, too. People who had VNS for depression told doctors they had less of an appetite.
The device targets nerve fibers in the vagus that tell your stomach when to empty and your brain when to feel full.
"We know there are certain nerve fibers that tell someone whether he's full or not, so let's just go straight to those and trick the brain into feeling full," George says. "Unlike a pill, it's just getting at stomach satiety signals."
The Maestro device also requires surgery, but it’s in the belly area instead. A July 2015 study in the Journal of Obesity found this implantable stimulator helps certain obese adults lose nearly 9% of their total body weight, and they keep it off at least 18 months. Researchers said there were mild or moderate side effects, including heartburn and belly pain.
The list price of the Maestro device is $19,000, although the company has been offering introductory pricing,according to Greg Lea, chief operating officer of EnteroMedics, which manufactures the device. It’s for use only in patients at obesity treatment centers who meet certain criteria, and is not covered by insurance.
Through clinical trials, more than 600 people have received the device, he says.
Hearing, Headaches, and More
Although only three vagal nerve stimulation devices are approved for use in the United States, the treatment is being investigated and moving into tests for other uses.
"We see it as a potential approach for all neurological and psychiatric disorders," says Mike Kilgard, PhD, a professor of neuroscience at the University of Texas at Dallas.
Here's a look at some of the ways hacking into the vagus nerve could transform modern medicine.
Researchers at UT Dallas are combining sound and vagal nerve stimulation to treat ringing in the ears, or tinnitus. A study involving 10 patients found the treatment eased symptoms in half of the group. The tinnitus device is already approved in Europe. Unlike the devices currently OK'd, it requires no surgery. Both the sound and stimulation are delivered through an external ear bud.
A study last year found that pairing nerve stimulation with physical therapy improves arm function in people who had a non-bleeding (ischemic) stroke. When you have a stroke, it can damage the part of the brain that helps you move. This new treatment enables another area of the brain to take over that movement. Researchers are now enrolling patients in the U.S. for further testing.
A handheld device to treat headaches is approved for use in Europe, but not yet in the United States. Users wave the device over their necks. Studies done in Europe show it helps lessen the pain of migraine and cluster headaches, and might even prevent them. Research so far suggests it works without any side effects.
The treatment may have the potential to treat ongoing and perhaps even sudden inflammation in the body.
Kevin J. Tracey, MD, president and CEO of the Feinstein Institute for Medical Research, discovered that stimulating the vagus in just the right way and at the right intensity prompts an anti-inflammatory reaction in the body. He's now testing it as treatment for people with rheumatoid arthritis and Crohn's disease, which involve body-wide (systemic) inflammation.
"In these conditions, the vagus nerve is not working well, it's firing too slowly. If this happens, your immune system overproduces [an inflammatory protein called] tumor necrosis factor [TNF], and that's bad for you," Tracey says. "What the VNS device does is slows the TNF."
Today, many people with Crohn's disease and rheumatoid arthritis take anti-TNF drugs to keep their symptoms under control. Tracey's research suggests that vagal nerve stimulation can have the same effect.
"We've had patients that don't have to take medications anymore, but it's going to take thousands of patients and years of experience to understand the outcomes,” he says.
Others in Europe are investigating the use of non-invasive or less-invasive vagus nerve stimulators in emergency rooms to halt asthma attacks. Asthma is due to inflammation in the lungs. Early studies show it's safe and that it improves moderate-to-severe asthma symptoms.
A Long List of Possibilities
Researchers are also testing the treatment in people who have:
Other potential uses for it that are being tested in animals right now include:
- Food allergies
The Future: Challenges and Hopes
Not all VNS results have been promising. For example, a 2014 study that looked at vagal nerve stimulation for heart failure didn't show a benefit. Studies for heart failure are ongoing.
To avoid the costs and complications from surgery, researchers are hoping to harness the power of the vagus from outside the body, via the ear or skin. Some worry you may not get a strong-enough signal from the nerve this way, but others, like ElectroCore Medical, which is developing the handheld device for headaches, remain confident.
In future, Tracey says you could also see the devices delivered by shot or maybe even rubbed on the skin or swallowed.
"At the end of the day, I think you will have a large number of patients in the future be treated with some type of implanted VNS device," he says. The devices "will be very small, they will talk to smartphones and computers, and your doctors will be treating you from nearby and far away."