Gamma Knife Surgery May Be Viable Alternative for Treatment of Intractable Epileptic Seizures

Caroline Cassels

October 20, 2006

October 20, 2006 (Chicago) -- Gamma knife radiosurgery (GKS) may offer a safe, effective, noninvasive alternative for the treatment of mesial temporal lobe epilepsy (MTLE), the most common cause of intractable epileptic seizures, a new study suggests.

At the American Neurological Association 131st Annual Meeting, Mark Quigg, MD, from the University of Virginia in Charlottesville, presented 2-year outcomes in seizure remission and cognition from the first multicenter, prospective pilot study of GKS.

"Based on these results, which are comparable to standard surgery, we believe there is now a promising, noninvasive alternative to anterior temporal lobectomy on the horizon," Dr. Quigg told Medscape.

The study, headed by Nicholas Barbaro, MD, from University of California, San Francisco, included 8 US centers and 30 unilateral MTLE patients. "These were patients with very clear, localizable unilateral temporal lobe epilepsy with as few confounders as possible. We chose these patients because we wanted the group to be a homogenous group of patients so we could get a clear picture of the procedure's safety and efficacy profile," he said.

Subjects were randomized to receive either low-dose (20-Gy) or high-dose (24-Gy) radiation GKS on mesial structures, including the amygdala, hippocampus, and parahippocampal gyrus.

At 24-month follow-up, the overall rate of seizure remission (defined as no seizures between the 18th and 24th postsurgical months) was 67%. However, among subjects in the high-dose group, seizure remission was 85%, vs 56% for the low-dose group.

Although the study was not designed to compare the statistical difference between the 2 study groups, Dr. Quigg said that the high-dose group appears to have the advantage in terms of seizure remission.

Secondary Outcomes

Investigators also looked at secondary outcomes, which included verbal memory, depression, and quality of life (QoL) and compared them with recent studies of open surgery.

Typically, said Dr. Quigg, one of the major neurocognitive consequences of open temporal lobectomy of the dominant side is a decline in verbal memory. Depending on the study, he added, a loss of verbal memory occurs in as many as 60% of patients. In his study, he said, about 42% of GKS subjects experienced a decline in at least 1 measure of verbal memory. On the other hand, he said, 25% of patients experienced an improvement in verbal memory.

While one of the major prospective open surgery studies showed an improvement in depression scores after patients were seizure free for 2 years, Dr. Quigg's group did not. However, he said, this may be a function of time. "Our seizure-free patients were only seizure free for 6 months. Perhaps given enough time, out data may look similar," he said.

QoL outcomes, Dr. Quigg said, came out as expected, with only seizure-free patients reporting an improvement. But, again, this may be due to the fact that duration of freedom from seizures is shorter in his study.

Low-Dose GKS Ineffective

Although promising, at this point, said Dr. Quigg, GKS is not ready for general use. Further research comparing open surgery with GKS is still required. Small case studies examining the efficacy of GKS published over the past 5 years have yielded dismal results. However, he added, these studies have all used low-dose radiation.

"We believe our study indicates that the low dose [of GKS] is a less-effective therapy. As we forge ahead, we're going to use the high dose and compare it directly with open surgery," he said.

If GKS proves to be viable alternative to open surgery, Dr. Quigg is optimistic that it will result in greater numbers of MTLE patients getting treatment. It is not uncommon, he said, for patients to reject open surgery because of fear of the procedure. Furthermore, he said, he believes open surgery is underutilized for MTLE because some neurologists also overestimate risk.

"If we can offer a noninvasive alternative that is as effective as open surgery and less expensive and addresses some of the shortcomings of anterior temporal lobectomy, maybe we can get more patients treated," he said.

ANA 131st Annual Meeting: Abstract S-95.

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