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May 3, 2005

Cochlear implants used for serious hearing loss

From: Detroit Free Press - Detroit,MI,USA - May 3, 2005


May 3, 2005

Hearing loss is one of the most common conditions among older adults. According to the National Institute on Deafness and Other Communication Disorders, it affects one-third of Americans older than 60 years of age and 40 percent to 50 percent of those 75 and older.

Common causes are the combined effects of loud noise, aging, prescription or illegal drugs, heredity and disease. Other culprits include wax buildup, a punctured eardrum and infection.

For some, hearing aids and certain medications can help. But for those who had a profound loss and got little benefit from other treatments -- both children and adults -- surgery is an option.

Called cochlear implantation, the procedure involves placing an electrical device inside the cochlea to stimulate the auditory nerve. Working in conjunction with a speech processor that sits behind the ear, it allows the perception of sound sensation.

"Cochlear implants have been around for 20 years in commercially available form," says Dr. Steven Telian, professor in the department of Otolaryngology and medical director of the University of Michigan's Cochlear Implant Program. The Food and Drug Administration approved devices for children in 1990. "They stimulate the nerve of hearing directly instead of using the outer and inner ear functions."

Different from a hearing aid, which amplifies sound, a cochlear implant compensates for damaged or nonworking parts of the inner ear. In normal hearing, parts of the inner ear convert sound waves in the air into electrical impulses. These impulses are then sent to the brain, where the hearing person recognizes them as sound.

A cochlear implant works in a similar manner, Telian says.

The components include:

•A microphone that picks up sounds from the environment.

•An external speech processor that selects and arranges those sounds.

•An external transmitter and internal receiver-stimulator that receive signals from the speech processor and convert them into electric impulses.

•An electrode that is implanted into the cochlea to collect impulses from the stimulator and send them to the brain.

To install the electrode, the surgeon must drill through the mastoid bone just behind the ear directly into the cochlea, a part of the inner ear that resembles a snail and is responsible for converting sounds from mechanical vibrations into electrical signals. The outer component is fitted just behind the ear and held in place by a magnet.

Telian says about 70,000 people worldwide have cochlear implants -- more than 1,000 of which were done at U-M. Still, he says, that's about 10 times less than the number who should have them. The problems are that the procedure is expensive, not widely available and under-reimbursed by insurance carriers.

Because of the cost -- between $30,000 and $50,000 per implant -- and the scarcity of public resources to support the procedure, doctors recommend that patients get only one.

Generally done as an outpatient procedure and under general anesthesia, the surgery takes three to four hours. Results are not immediate.

Telian says patients must heal for 30 days before the external transmitter can be fitted and programmed. After that, they will likely need speech and other auditory training. Initial improvements in hearing are recognized about three months after the tuning session and continue over several years.

Doctors say generally children are slower to adapt to the new sounds than adults and need a lot more training.

"It's not natural hearing because it's electronic," Telian says. "Some people who have had normal hearing in the past say it's cartoonish. But with adjustments, they can eventually tell male and female voices, talk on the phone, recognize different sounds."

Like any surgery, Telian says, this one has risks.

"The most common thing is that the internal device can fail electronically," he says, adding that statistics show that has happened in only 2 percent of cases in the last decade. In addition, one in 200 patients get some kind of infection. There is a risk of facial nerve injury, too.

Fortunately, he says, so far the technology has proved itself with very few problems. But because the procedure is still relatively new, it's unclear how long the implants last.

"We have patients who've had these devices for 20 years so far," he says.

Copyright © 2005 Detroit Free Press Inc.