Help for Those with Movement Disorders Activa System implant and other technologies offer help for those suffering from uncontrollable shaking in diseases like Parkinson's From: Design News, Lifesavers: The Components behind Today's Medical Breakthroughs - May 5, 2003 - page 9 By: Amy Castor The uncontrollable and sometimes violent shaking that accompanies Parkinson's and another movement disorder called "essential tremor" can rob its victims of the ability to do simple tasks. In 1997, new hope arrived when the Food and Drug Administration (FDA) approved Medtronic's Activa system, a device that blocks the errant brain signals responsible for the symptoms. Since Design News first reported on Activa four years ago, the device has evolved, gained new FDA approvals for its use, and gathered momentum for use in treating other movement disorders, along with obsessive compulsive disorder and epilepsy. Today, 10,000 people throughout Europe, Canada, and Australia have an Activa system implant. For the nearly 650,000 people in the U.S. who suffer from Parkinson's, the device brought a welcome option to drug treatments that lose their effectiveness over time and surgeries that permanently destroy brain tissue. A reversible procedure, the Activa works by delivering mild electrical pulses to targeted areas of the brain to block the signals that cause the symptoms. Caption 1: A new device called Kenatra (not shown), up for FDA approval, will eliminate the need for two pulse generators to stimulate both sides of the brain in patients who require tremor control on both sides of the body. Through its upgrades, the inner workings of Activa remain the same: An insulated electrical lead is surgically implanted in a targeted area of the brain‘s thalamus. From it, an insulated extension wire threads out under the skin of the head, neck, and shoulder to an implanted pulse generator just below the collar bone. The pulse generator sends a constant stream of tiny electrical pulses to thalamus. Once the system is implanted, the user can turn the device on and off at will or change the setting from low to high stimulation by moving a hand-held magnet over the pulse generator. An external computer allows doctors to make minor adjustments to the system noninvasively. Hardware Updates Some of the advancements in Activa are minor, but worthy of mention. They include an 25% thinner extension wire, which makes it less noticeable and more comfortable for the patient. Spacing between the four electrodes in the lead is reduced from 1.5 to 1.0 mm, allowing it to reach smaller brain targets. And replacing the briefcase-sized computer used to program Activa is an N'Vision programmer that resembles a supersized PDA. Using telemetry to communicate to Activa, the device allows clinicians to alter various settings of the pulse generator by touching the screen with a stylus. More Updates Are Pending Medtronic is crossing its fingers in hopes that by this summer the FDA will approve use of a bidirectional implanted pulse generator. The new device, called Kinetra, replaces the need for two pulse generators in patients who want two Activa systems to reduce tremors on both sides of the body. Kinetra accepts two leads and two extensions. For the patient, this means less cost, fewer implants, and less time on the operating table. The device also leaves room on the right side of the chest for cardiac assist devices, should the patient ever need one. "Kinetra has been selling for three years in Europe," says Lynn Otten, senior principal design engineer for Activa. "But releasing products in Europe is substantially easier then in the U.S." Further out on the Activa timeline is Restore, a rechargeable battery for the implanted pulse generator that would eliminate the need for battery replacement surgery. The 9V battery in Activa lasts about five years. Currently, Restore is undergoing clinical testing in cadavers. "We're looking at bioacceptability and doing testing to determine where on the skull to place these things that would be the least traumatic if a person were in a car accident or got hit in the head," says Otten. "All these questions need to be answered before we even go to fixed prototypes." She expects the device to hit the market in five to six years. Otten gets excited in talking about a new technology currently in testing at three U.S. clinics called "active MRI," which allows the surgeon to place the lead into the brain a real time without the use of a head frame. Normally, heavy stereotactic titanium frames are screwed onto the patient's skull prior to taking the MRI. Extremely uncomfortably, these frames provide a coordinate system for localizing targets. Not only are active MRIs a blessing to the patient, but they open a door to understanding how Activa works. Caption 2: Replacing the briefcasesized computer used to program Activa is an N'Vision programmer. Caption 3: The implantable impulse generator, shown here, is similar to a cardiac pacemaker. It generates electrical signals that are delivered to the brain via a thin, implanted coiled wire with electrodes attached at the tip. In Parkinson's, cells die in the substantia nigra, a corner of the brain that produces dopamine, a neurotransmitter that allows communication between brain cells involved in the control of movement. The reduced levels of dopamine lead to the symptoms of Parkinson's. Some theories suggest that Activa works by enhancing dopamine receptor cells to better absorb dopamine, but no one is sure. "Right now nobody knows how Activa works,", says Otten. "All we know is that it works, and when we shut it off, it doesn‘t work." Other Benefits Patients suffering from other types of movement disorders also may soon be finding relief in Activa. Right now there are 250 patients in Europe using Activa to treat Dystonia, the third most common movement disorder outside of Parkinson's and essential tremor. Often occurring in children, Dystonia is a syndrome of sustained muscle contractions that cause twisting, repetitive movements, or abnormal postures. "The results are phenomenal," says Otten. "You go from a contorted, screaming child who drags himself along the floor to one who is running marathons." There's also a pocket of studies going on with Activa and obsessive compulsive disorder with "interesting to good results." And Activa is now being tested on epilepsy patients, using a combination of blocking and sensing technologies. Shrinking Technology The future for Active looks bright, but tiny. "We‘re looking for total miniaturization of the system," says Otten. Although tight-lipped about the technical details, she says that as soon as five years we may be seeing a system that is entirely implantable and fits completely inside the patient's head. "You won't have to do anything with the chest walls anymore, and no more wires dangling through the neck," she says. Prototypes exist, she says, and are currently being tested on cadavers. Caption 4: Medtronic developed a new extension, which threads under the skin of the head, neck, and shoulders. The thin, implanted coiled wire is 25% thinner than its predecessor, giving it a lower profile and making it more comfortable for patients.