Fast ripples could guide epilepsy resection
medwireNews: Residual fast ripples predict recurrent seizures after surgery for epilepsy and could guide intraoperative tailoring of the resection, a study suggests.
Maryse van ’t Klooster (University Medical Center Utrecht, the Netherlands) and co-workers found that three-quarters of patients with residual fast ripples, defined as high-frequency oscillations of 250 to 500 Hz, after resection had recurrent seizures.
By contrast, residual ripples of 80 to 250 Hz, interictal spikes and ictiform spike patterns were not associated with recurrence.
In an editorial accompanying the study in Neurology, Barbara Jobst (Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA) and Jerome Engel Jr (David Geffen School of Medicine at UCLA, Los Angeles, California, USA) say that if further research confirms fast ripples as biomarkers for the epileptogenic area, they “could provide a simple solution for a longstanding clinical problem.”
They call for more research into the underlying mechanisms of high-frequency oscillations, “not only to improve their value as biomarkers, but to identify potential targets for novel approaches to treat seizures and prevent and cure epilepsy.”
Of the 54 patients included in the study, 24 (44%) had recurrent seizures during a median 25 months of follow-up after surgery, although 80% of these individuals did achieve a worthwhile improvement.
Intraoperative electrocorticography, performed after the resection, showed residual fast ripples in 12 patients, nine of whom had recurrent seizures. This gave residual fast ripples a positive predictive value of 75.0% and a negative predictive value of 64.3%.
Of the three patients who were seizure-free, one had not yet attempted to reduce their anti-epileptic drug dose. The researchers note that two patients with fast ripples were free of seizures for the first year after resection, but had recurrence when they reduced their medication dose.
They say: “We hypothesize that removing the majority of pre-resection [fast ripples] might be enough to achieve improvement in disease severity (i.e., Engel 1B-2), but that complete removal of [fast ripples] is necessary to achieve true long-term seizure freedom.”
Six patients had fast ripples at the border of the resected area, five of whom had recurrent seizures. The team says that they could have extended the resection area in five of the six patients “without compromising eloquent regions”. Removal of more tissue was also possible in three of six patients with fast ripples in areas beyond the resection margins.
But the researchers caution that the effect of resection extension on outcome is not clear, and note that they found residual fast ripples in functionally eloquent areas in two of the three patients who achieved freedom from seizures. This suggests that some fast ripples “might be physiologic as well”, they say.
All patients with recurrent seizures had residual ripples, but so did 27 of the 30 patients who achieved freedom from seizures, so ripples did not predict recurrence. Likewise, 18 patients with versus 20 without recurrence had residual spikes and four with versus five without recurrence had ictiform spike patterns.
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