FDA today approved an expanded use of a brain implant to help control some symptoms of advanced Parkinson's disease.

The device, a deep brain stimulator, made by Medtronic, Inc., of Minneapolis, Minn., was initially approved by FDA in 1997 for use in one side of the brain to help control tremors on one side of the body.

Today, after review of additional studies conducted by the manufacturer, the agency approved the device, called the Activa Parkinson's Control System, for use in both sides of the brain to help reduce some of the other symptoms of advanced Parkinson's that cannot be adequately controlled with medication.

An estimated 1.5 million Americans have Parkinson's disease, which results in tremors, rigidity, postural instability, slowness and difficulty moving and, in some people, intellectual deterioration.

The Activa system consists of electrodes that are implanted into the brain and connected by leads (wires) under the skin to a pulse generator implanted in the abdomen or chest. The pulse generator sends a constant stream of tiny electrical pulses to the brain, blocking tremors. When the device is implanted in both sides of the brain, two separate systems are used.

To turn the stimulator on and off, the patient holds a magnet over the pulse generator. The generator must be replaced every three to five years, the life of the battery.

FDA based approval of the device on a clinical study conducted by Medtronic of the system's safety and effectiveness when implanted in both sides of the brain and on the recommendation of the Neurological Devices Panel of FDA's Medical Devices Advisory Committee.

Some 160 patients with advanced Parkinson's disease were enrolled at 18 medical centers in the United States, Canada, Australia and Europe. The device was implanted bilaterally in 134 patients. The implant procedures were done simultaneously or in stages. The patients were followed for approximately one year.

During the study, patients were evaluated for a variety of Parkinson's symptoms using a test for total motor skills, including hand movement, leg agility, facial expression, rigidity, tremor and speech. They were tested with the Activa system turned on, both with and without medication. Total motor skills improved in nearly half the patients taking medication and approximately 90 percent of the patients not taking medication.

In addition, diary data from a subset of 64 patients in the study showed that the Activa device increased good motor function and relief from Parkinson's symptoms by an average of six hours a day. And it decreased by an average of three hours a day the amount of time the patients experienced abnormal, involuntary movements such as a waving of arms.

Although some patients in the study benefited significantly from the Activa system, the study also showed that individual results varied considerably and specific benefit for an individual cannot be predicted.

Nearly all of the 160 patients enrolled in the study experienced one or more adverse events. During the entire study, 7.5 percent had bleeding into the brain; 11 percent had device-related infection; 10 percent had paralysis, and 8 percent had weakness.

Some 37 percent of the adverse events, such as breakage of the lead, pain and infection, were related to the Activa system. Six percent of the device-related adverse events were serious and ongoing, including a worsening of motor impairment and other Parkinson's symptoms.

Medtronic has agreed to conduct a three-year, post- approval study of the system to assess its long-term clinical results.