Effect of invasive EEG monitoring on cognitive outcome after left temporal lobe epilepsy surgery

Abstract

Objectives: The objective of this cohort study was to compare neuropsychological outcomes following left temporal lobe resection (TLR) in patients with epilepsy who had or had not undergone prior invasive monitoring.Methods: Data were obtained from an institutional review board-approved, neuropsychology registry for patients who underwent epilepsy surgery at Cleveland Clinic between 1997 and 2013. A total of 176 patients (45 with and 131 without invasive EEG) met inclusion criteria. Primary outcome measures were verbal memory and language scores. Other cognitive outcomes were also examined. Outcomes were assessed using difference in scores from before to after surgery and by presence/absence of clinically meaningful decline using reliable change indices (RCIs). Effect of invasive EEG on cognitive outcomes was estimated using weighting and propensity score adjustment to account for differences in baseline characteristics. Linear and logistic regression models compared surgical groups on all cognitive outcomes.Results: Patients with invasive monitoring showed greater declines in confrontation naming; however, when RCIs were used to assess clinically meaningful change, there was no significant treatment effect on naming performance. No difference in verbal memory was observed, regardless of how the outcome was measured. In secondary outcomes, patients with invasive monitoring showed greater declines in working memory, which were no longer apparent using RCIs to define change. There were no outcome differences on other cognitive measures. Conclusions:Results suggest that invasive EEG monitoring conducted prior to left TLR is not associated with greater cognitive morbidity than left TLR alone. This information is important when counseling patients regarding cognitive risks associated with this elective surgery. Temporal lobe epilepsy is the most frequent type of epilepsy encountered in surgical centers, 1 and resective surgery is an effective treatment option for patients with drug-resistant seizures.

Histopathologic subtype of hippocampal sclerosis and episodic memory performance before and after temporal lobectomy for epilepsy

“…Among the subset of patients who returned after surgery, postoperative testing was completed an average of 8.1 months (SD 7.8) after surgery and 12.2 (SD 8.7) months after the preoperative evaluation. The average retest interval in the current study was longer than the 7.5 month (SD 3.3) average retest interval used by Martin et al for development of the RCIs, but in line with the case example used by Martin et al (ie, 11 months) and with patient samples from other studies that have characterized cognitive outcome using these RCIs …”

“…The average retest interval in the current study was longer than the 7.5 month (SD 3.3) average retest interval used by Martin et al 16 | 827 studies that have characterized cognitive outcome using these RCIs. [17][18][19]…”

The immediate and short‐term effects of bilateral intrahippocampal depth electrodes on verbal memory

“…Ljung et al consider their study to be the first demonstrating verbal memory decline due to intrahippocampal depth electrodes. The findings contrast with studies that did not find negative cognitive effects of depth electrodes, invasive electroencephalographic (EEG) monitoring, or deep brain stimulation . However, the well‐known “placement effect” after implantations for deep brain stimulation within other target structures shows that the implantation itself can have a considerable functional effect, which seems transient but can cause measurable cognitive impairment …”

Cognitive safety of intracranial electrodes for epilepsy

“…No studies have specifically examined the cognitive effects of longitudinal parasagittal vs lateral orthogonal hippocampal implantations in patients undergoing preoperative surgery evaluation, much less other types of iEEG. Busch et al addresses only patients undergoing left temporal lobe surgery, showing no effect of preoperative iEEG in these patients postoperatively, a finding consistent with left temporal lobe patients in Helmstaedter et al…”

“…The third study was conducted by Busch et al, who enrolled 176 patients with left TLE (131 without and 45 with various types of iEEG of which 37 had depth electrodes; the types of depth electrodes were not listed). The primary verbal memory measure was the Wechsler Memory Scale‐III Immediate and Delayed Auditory Memory Indices.…”