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A Judicious Jolt for Seizures

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Fall 2003
Volume 16, Number 2

The light at the end of epilepsy's tunnel has been all too dim," says neurologist Gregory Bergey, M.D., who probably could fine-tune patients' medications in his sleep. "We've seen nine new drugs in the last decade, but if you fail two or three of them, chances of a fourth ending your seizures is only about 5 percent. Yes, we're better at matching medicines and patients, but are we keeping many more from having seizures? I doubt it."

Gregory Bergey, M.D.
"ERNS is both light and thin."
says Gregory Bergey of the
stimulator he is showing
patient Mary Scott.

Yet if approaches pan out, real change will come, he says. "And none too soon."

The method Bergey is shepherding reflects recent thought that mildly zapping the CNS with electrical currents can be therapeutic. "Seizures are an abnormal brain excitation that we've countered with inhibitory drugs. But new ideas on how seizures begin and propagate are leading us to try to disrupt them with an excitatory stimulus."

ERNS, the implanted External Responsive Neurostimulator System, for example-a device half the size of a Ritz cracker-delivers currents in response to seizures. A computer chip is "tuned" to detect a seizure pattern specific for each patient, sensing the earliest seconds of wayward activity. Then, the researchers say, the brief, mild stimulus that's released should disrupt or stop the seizure. In the 1 to 4 milliamp range, the stimuli appear safe-even with repeated application. And patients can't feel the stimuli.

ERNS rests in a cavity in the skull. Only the electrodes of its attached probe touch the target brain surface.

Early on, Hopkins work helped verify ideas that underlie the system. Bergey's team, for example, showed that each patient has a consistent pattern of seizure onset. And his team's computer models of seizures bolstered the idea that stimulation could turn them off. Now Hopkins is collaborating with several other major centers in testing the first implants of the device.

ERNS isn't like vagus nerve stimulation (VNS), which routinely jolts the nerve every five minutes, indirectly altering brain activity that could sum to cause seizures. "VNS rarely makes patients seizure free," Bergey explains, "and a good outcome only halves their frequency. You still can't drive! With ERNS, we're looking at responsive stimulation directed at each seizure. Our hopes for the studies are high."

For more information, call 410-955-7338.



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