Interictal epileptiform discharge effects on neuropsychological assessment and epilepsy surgical planning

Abstract

Both animal and human research suggests interictal epileptiform discharges (IEDs) may affect cognition, although the significance of such findings remains controversial. We review a wide range of literature with bearing on this topic, and present relevant epilepsy surgery cases, which suggest the effects of IEDs may be substantial and informative for surgical planning. In the first case, we present an epilepsy patient with left anterior temporal lobe (TL) seizure onset who experienced frequent IEDs during preoperative neuropsychological assessment. Cognitive results strongly lateralized to the left TL. Because the patient failed performance validity tests and appeared amnestic for verbal materials inconsistent with his work history, selected neuropsychological tests were repeated 6 weeks later. Scores improved one to two standard deviations over the initial evaluation, and because of this improvement, were only mildly suggestive of left TL impairment. The second case involves another patient with documented left TL epilepsy who experienced epileptiform activity while undergoing neurocognitive testing and simultaneous ambulatory EEG recording. This patient’s verbal memory performance was impaired during the period that IEDs were present but near normal when such activity was absent. Overall, although the presence of IEDs may be helpful in confirming laterality of seizure onset, frequent IEDs might disrupt focal cognitive functions, and distort accurate measurement of neuropsychological ability, interfering with accurate characterization of surgical risks and benefits. Such transient effects on daily performance may also contribute to significant functional compromise. We include a discussion of the manner in which IED effects during presurgical assessment can hinder individual patient presurgical planning as well as distort outcome research (e.g., IEDs occurring during presurgical assessment may lead to an underestimation of postoperative neuropsychological decline).

Brain regions and epileptogenicity influence epileptic interictal spike production and propagation during NREM sleep in comparison with wakefulness

“…The increased IS activity during NREM sleep could have functional consequences. The role of interictal activity in cognitive deficit is still controversial . We could hypothesize from our result that the predisposition of the MTL region for increased IS activity during sleep might have a deleterious impact on cognition, especially in memory.…”

Inhibiting Epileptiform Activity in Cognitive Disorders: Possibilities for a Novel Therapeutic Approach

“…IEA and SEA both recorded mainly over the frontotemporal areas in AD ( Rao et al, 2009 ; Vossel et al, 2013 , 2016 ; Cretin et al, 2016 ; Sarkis et al, 2016 ; Horváth et al, 2018b ), in ADHD ( Lee et al, 2016 ), and in ASD ( Chez et al, 2006 ). Frequent occurrence of interictal discharges associate to decreased therapeutic response, poorer postsurgical outcome, and augmented cognitive decline in epilepsy patients ( Drane et al, 2016 ). Higher frequency of IEA in SWS defines more prominent impairment in language function of epileptic patients with ESES ( Scheltens-de Boer, 2009 ).…”

Hippocampal MRS and subfield volumetry at 7T detects dysfunction not specific to seizure focus

“…The subiculum has also been proposed as a potential generator of interictal discharges in cell recordings of resected TLE hippocampal tissue 45 , 46 . Interictal discharge activity directly contributes to memory disruption in TLE 47 and poses an important confound in evaluations aiming to predict surgical memory outcomes from pre-operative performance. Our data linking subicular volume loss with impaired preoperative story recall may potentially offer an additional means to discriminate transient interictal discharge effects from likely irreversible network disruption in surgical TLE candidates.…”