Nerve "Pacemakers" Are Changing Lives
Parkinson's disease used to make Paige Brenner's left hand shake so much that it took her 20 minutes to put her hair in a ponytail. Then, surgeons at St. Joseph's Hospital in Phoenix implanted a device that delivers a mild electrical shock to an area of her brain responsible for movement. Now she does her hair in 20 seconds. Indeed, the moment doctors activated the implant via radio control, her tremor became barely noticeable. "It was like flipping a light switch," says Brenner, a 31-year-old archivist for TSG Publishing in Cave Creek, Ariz.
We're all familiar with cardiac pacemakers, which send rhythmic electrical impulses to the heart to regulate its beat. Now doctors are implanting similar devices in the brain and along the spine to treat a range of neurological disorders. Making this possible is a better understanding of the electrical and chemical nature of the nervous system, faster and cheaper microchips, and the advent of real-time imaging technologies that pinpoint the placement of electrodes.
The Food & Drug Administration has approved neurostimulation devices for use in the treatment of Parkinson's disease, epilepsy, chronic pain, and incontinence. But researchers are studying the technique to control obesity and depression as well. These treatments offer new hope to patients who have failed to respond to easier, less invasive procedures. The cost of surgically implanting and maintaining the devices--including equipment, doctor's fees, general anesthetic, and a few days' stay at the hospital--can range from $20,000 to $50,000. But it's usually covered by insurance. Appliances such as microwaves and cell phones won't interfere with an implant's function, although a device could set off a metal detector.
The devices have three basic components: electrodes, wires, and a battery-powered pulse generator. The placement of these parts differs according to the disorder. For Parkinson's, surgeons drill a half-inch hole in the skull and, guided by real-time magnetic resonance imaging machines (MRI), thread a lead with electrodes to the point in the center of the brain responsible for movement. The electrodes get their charge via wires running under the skin, down the skull and neck, to a stopwatch-size pulse generator in the chest.
In Parkinson's, the nerves in the brain fire too often because the body lacks an inhibitory chemical called dopamine. It's not clear why sending periodic, electrical charges into the brain eases the tremors and rigidity that mark the disease. The pulses may interrupt the abnormal firing patterns, or maybe they prompt inhibitory neurons to do so. "No one really knows why it works, but it works," says Dr. Erwin Montgomery, co-director of the Cleveland Clinic's Center for Functional & Restorative Neurosciences. He says 75% of Parkinson's sufferers who get implants see a marked improvement.
STIMULATING. The reasons neurostimulation helps reduce the frequency of epileptic seizures also are poorly understood. To treat epilepsy, a pulse generator is implanted in the chest, while the electrodes are attached to the vagus nerve in the neck, which carries information from the vascular and digestive systems to the brain. The periodic pulses transmitted through the vagus may condition the brain to deal with the electrical disruptions that cause seizures, according to one theory. Dr. Jerome Murphy, chief neurosurgeon at Children's Mercy Hospital in Kansas City, Mo., says half of all patients with an implant generally suffer 50% fewer seizures, adding that it creates a "dramatically improved quality of life." Just ask Colleen Thurnherr of Lancaster, N.Y. Her daughter, Jordan, 9, got an implant five months ago and has gone from suffering multiple seizures every night to very short seizures every couple of nights. "Jordan is not falling asleep in school and has the energy to rollerblade and ride a bike," Thurnherr says.
Stimulating the vagus also shows promise in treating depression and obesity. A 30-patient, three-month study on the effect of vagus nerve stimulation (VNS) on depression sufferers was coordinated last year by the University of Texas Southwestern Medical Center in Dallas. Some 40% of patients reported at least a 50% improvement in symptoms. A 200-patient study will begin this summer. Meanwhile, researchers at Maimonides Medical Center in Brooklyn, N.Y., found that dogs lost 25% to 30% of their body weight when an electrode was attached to the vagus nerve. Human clinical trials may begin as early as July.
While researchers are still trying to determine whether neurostimulation can affect appetite, one area where it has made strides is in controlling severe chronic pain. Advances in microchip technology have led to fully implantable devices that doctors can program to deliver complex pulse patterns at various frequencies and voltages. In the past, pain treatments used external or partially implanted devices. To treat chronic pain in the neck, back, or extremities, surgeons position electrodes just above sites along the spinal cord that get pain signals from the afflicted body part. The pulse generator is usually put under the skin in the lower abdomen.
IN CONTROL. Electrical stimulation also can help people who have uncontrollable urges to urinate because their bladders are constantly contracting. Doctors implant a generator in the lower abdomen and attach electrodes to the sacral nerves at the base of the spinal column. When the nerves are stimulated, the pelvic muscles tighten, allowing the bladder to relax. Neurostimulation also helps those who can't empty their bladder completely and those who feel the need to urinate all the time. The success rate is about 70%.
Neurostimulation's main side effect is a tingly feeling where the electrodes are attached. Other problems include infection and a strained-sounding voice when the vagus nerve, which connects to the larynx, is stimulated. While the implants can stay in the body almost permanently, the battery-powered generator must be replaced every five to eight years depending on the pulse intensity and frequency. Replacing the generator can be done in the doctor's office under local anesthesia; its $8,500 to $10,000 cost is generally covered by insurance. Most devices can be controlled externally, allowing patients to adjust settings or shut them down. But doctors say most patients feel so much better with their implants on that they never want to turn them off.