Last week, a man from Yakima, Washington, became the first patient to receive an implant designed to quell the disabling attacks of vertigo that result from a condition known as Meniere's disease. The device, developed by researchers at the University of Washington, is the first therapeutic implant to treat a disorder of the vestibular system, a set of organs in the inner ear responsible for sensing head motion and maintaining balance. The researchers hope that the device will not only help treat the disease but also pave the way for more complex devices for balance disorders.
New role: A new vestibular implant is based on this cochlear implant. But rather than treating deafness, it treats disorders of the inner ear.
People with Meniere's disease experience sudden attacks that can include intense dizziness, tinnitus, nausea, and hearing loss. The attacks can last from 30 minutes to several hours, and may happen every few years to every day. There is no cure, although the condition can sometimes be treated with medications and dietary restrictions. In very severe cases, patients opt to destroy the function of the inner ear through surgery or medical treatment.
The inner ear contains a set of three structures called the semicircular canals, which function like a gyroscope by detecting the movement of fluid through the canals to sense the rotation of the head. Jay Rubinstein, an ear surgeon and otolaryngologist at the University of Washington Medical Center, explains that the brain normally receives constant input about head movement from the vestibular nerves, which are connected to each of these structures, as well as two other structures that sense horizontal and vertical movement.
Doctors believe that during a Meniere's attack, fluid buildup in the inner ear blocks the information from the nerves in one ear, leading the brain to think that the body is turning. The implant works by electrically stimulating the vestibular nerves attached to the semicircular canals of the compromised ear during an attack, thereby compensating for the missing signal. The new implant is a modification of a cochlear implant whose design and surgical implantation had already been approved by the FDA. The modified one consists of a surgically implanted device that contains three electrode arrays: each one is inserted into one of the semicircular canals. An external processor, worn behind the affected ear, communicates wirelessly with the internal component. When experiencing an attack, the patient can manually activate the device. At other times, it remains off. Although the device requires surgical implantation, it does not require disabling a patient's balance system or pose the threat of hearing loss, which is the case with some of the more radical treatments for severe Meniere's disease.
After conducting initial experiments in monkeys, Rubinstein and a collaborator, James Phillips, received approval for a 10-person clinical trial of the device, which is manufactured by the Australian company Cochlear. So far, the Yakima patient is the only one who's received the device; the team has funding to implant devices in two additional patients. Rubinstein says it may take some time to evaluate the effectiveness, because the timing of Meniere's attacks is unpredictable.
Daniel Merfeld, a balance researcher at Massachusetts Eye and Ear Infirmary who was not involved in the work, says that this device represents "a first step toward the long-term goal of sensory replacement via a vestibular implant." A handful of groups in the United States and Europe, including Merfeld's, have been working on a prosthetic device that would help people with balance disorders of the inner ear, similar to the way a cochlear implant allows deaf people to hear sounds. A cochlear implant picks up sounds from the environment and translates them into electrical signals that stimulate the auditory nerves.
In simple terms, a vestibular implant would replace the microphones of an auditory implant with motion sensors, and adapt the electrical signals for the vestibular nerves. The devices would sense motion of the head and translate that sensory information into electrical impulses. Merfeld says that each team has had good results in animals, and that the goal of replacing the sense of balance seems technically feasible in the next several years. "What's needed is a lot of research and some successful clinical trials," he says.
In the meantime, the current device is an intermediate step in that process, as it does not sense or adapt its signals to head motion and does not replace the body's own balance system, but is merely designed to override the function of the ear as it recovers from an attack. Rubinstein says that such a device is an attractive first foray into vestibular implants because it does not destroy existing function and does not require regulatory approval of a totally novel device.
By Courtney Humphries
From Technology Review