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Investigators reported that six of seven patients with temporal lobe epilepsy who underwent stereotactic laser ablation guided by MRI had better episodic memory outcomes compared with patients who underwent open resection.
Patients with temporal lobe epilepsy (TLE) who underwent stereotactic laser ablation guided by MRI had better episodic memory outcomes compared with patients who underwent open resection, according to data presented at the American Epilepsy Society (AES) annual meeting earlier this month.
The findings underscore the technique's potential for eradicating or limiting seizure activity in TLE patients — with the caveat that only a limited number of laser-surgery patients have been studied so far.
Laser ablation is minimally invasive, and most patients go home the next day, said Daniel Drane, PhD, assistant professor of neurology at Emory University School of Medicine, who reported results for seven patients who had had laser ablation.
Investigators reported that just one out of the initial seven laser-ablation patients experienced any significant decline in memory. Each patient was evaluated on two standard episodic memory tasks before and after surgery, one assessing visual memory (recall of simple geometric figures) and one assessing verbal memory (list learning). Investigators noted that the patient with the verbal memory decline had undergone right hippocampal ablation but later presented with seizures from the left temporal lobe, leading them to think that the decline is related to the new region of seizure onset rather than the surgery.
“The left side of this patient's brain was known to control language,” said Dr. Drane, “so it would be unlikely for him to experience verbal memory decline following any type of procedure involving the right side of his brain.” In addition, six of seven laser ablation patients experienced significant improvement on one or more of these memory measures, which sometimes included improvements on the type of memory related to the side of surgery.
Patients who underwent open surgical resections — including nine selective amygdalohippocampectomies and one procedure that resected mesial and anterolateral regions — had much worse cognitive outcomes, with nine out of 10 experiencing a significant decline in one or both memory tasks. Unlike the patients undergoing laser ablation, only four of 10 patients experienced any significant memory improvement, and none had improved memory associated with the side of surgery.
Dr. Drane believes that the laser surgery results in better naming and object recognition outcomes because the laser ablation avoids damage to key pathways and structures normally included in open resections. He speculated that laser surgery may provide the patient with a better opportunity for functions to reorganize after surgery. Memory outcomes may also vary by the extent of hippocampal pathology, as only two of the seven patients undergoing laser ablation lacked hippocampal sclerosis.
With regards to seizure outcome, investigators reported that there were no significant differences between the two surgical methods: four of seven (57.1 percent) of the laser ablation patients were seizure free at 6 months, while 5 of 10 (50 percent) of the “standard” surgery patients were seizure free at the same time point (6 months).
While percentages quoted for open resections are typically higher (for example, 65–75 percent), Dr. Drane pointed out that the investigators presented data for “all comers,” rather than the more tightly selected population often used in other temporal lobe resection outcome studies. Using more selective criteria yields better results for both surgical groups but is less likely to reflect real-world experience.
Robert E. Gross, MD, PhD, professor of neurosurgery at Emory, said the laser-ablation approach will not work for everyone, as some patients clearly have seizure onset zones that are broader in nature. However, he adds that it has shown good results in a number of patients already.
Commenting on the study limitations, Dr. Drane noted that the study included a very small sample size and needs to be replicated in other centers.
Shlomo Shinnar, MD, PhD, director of the Comprehensive Epilepsy Management Center at Montefiore Medical Center, said the findings are intriguing.
“This study demonstrates that, in a small sample of patients with a short duration of follow up, they appear to have favorable outcomes including relative preservation of neuropsychological function,” he said. “However, one must sound a note of caution that these were not part of a randomized clinical trial... While these data suggest the need for a larger trial, it is premature to conclude that this procedure should be preferred over standard temporal lobectomy.”
He said that, when offering patients the option of laser ablation, that the option be described appropriately. “The question is, are you telling them already it works as well and you'll have less memory deficit and it's less major surgery... or it's a novel procedure it may work as well, it may have less memory deficits, but it's still new and only been done in a small number of patients.”
Longer-term follow up will be important, he said.
“We know that with standard temporal lobectomy for hippocampal sclerosis the remission rate starts dropping off once you get past five, seven years,” he said. “You want at least two, three years of follow-up. If you make them seizure free for two years — two, three years — you're probably doing a good job at abolishing whatever that circuitry is, but six months is kind of short.”
It's also important to look at patient mix, ideally comparing cases with similar severity and complexity, as well as baseline cognitive function, since those with higher function at baseline will tend to see a higher drop-off. More research is needed, he concluded.
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