Correspondence between large‐scale ictal and interictal epileptic networks revealed by single photon emission computed tomography (SPECT) and electroencephalography (EEG)–functional magnetic resonance imaging (fMRI)

Abstract

SUMMARYObjective: Epilepsy is increasingly recognized as a network disorder, but the spatial relationship between ictal and interictal networks is still largely unexplored. In this work, we compared hemodynamic changes related to seizures and interictal spikes on a whole brain scale. Methods: Twenty-eight patients with refractory focal epilepsy (14 temporal and 14 extratemporal lobe) underwent both subtraction ictal single photon emission computed tomography (SPECT) coregistered to magnetic resonance imaging (MRI) (SISCOM) and spike-related electroencephalography (EEG-functional MRI (fMRI). SISCOM visualized relative perfusion changes during seizures, whereas EEG-fMRI mapped blood oxygen level-dependent (BOLD) changes related to spikes. Similarity between statistical maps of both modalities was analyzed per patient using the following two measures: (1) correlation between unthresholded statistical maps (Pearson's correlation coefficient) and (2) overlap between thresholded images (Dice coefficient). Overlap was evaluated at a regional level, for hyperperfusions and activations and for hypoperfusions and deactivations separately, using different thresholds. Nonparametric permutation tests were applied to assess statistical significance (p ≤ 0.05). Results: We found significant and positive correlations between hemodynamic changes related to seizures and spikes in 27 (96%) of 28 cases (median correlation coefficient 0.29 [range À0.12 to 0.62]). In 20 (71%) of 28 cases, spatial overlap between hyperperfusion on SISCOM and activation on EEG-fMRI was significantly larger than expected by chance. Congruent changes were not restricted to the territory of the presumed epileptogenic zone, but could be seen at distant sites (e.g., cerebellum and basal ganglia). Overlap between ictal hypoperfusion and interictal deactivation was statistically significant in 22 (79%) of 28 patients. Despite the high rate of congruence, discrepancies were observed for both modalities. Significance: We conclude that hemodynamic changes related to seizures and spikes varied spatially with the same sign and within a common network. Overlap was present in regions nearby and distant from discharge origin.

Dysfunction of Neurovascular/Metabolic Coupling in Chronic Focal Epilepsy

“…A summary of equations of the model was provided in Table I. Taking into consideration previous reports about possible dysfunctions in the hyperemic response and oxygen metabolism in epileptogenic cortices [3][4][5][6][7][8][9], parameters ε and κ are of great interest in our study. ε is an unknown parameter in the model relating neuronal activity to the CBF.…”

“…The pathogenic relationships between the irritative zones and the seizure-onset zones are poorly understood in focal epilepsy [8]. Nevertheless, IEDs are accepted as specific EEG markers of interest for presurgical evaluation of epileptic patients, because they are very frequent paroxysmal and asymptomatic events, are easily recorded and provide high specificity for localizing seizureonset zones [9].…”

Periodic lateralized epileptiform discharges can survive anesthesia and result in asymmetric drug-induced burst suppression

“…Nonetheless, some studies have shown that focal hypermetabolism and/or hyperperfusion may also occur during focal interictal spikes. 20,21 Electrographic seizures may emerge during PLEDs, coexist with PLEDs, or evolve on top of PLEDs 10,14 suggesting that seizures and PLEDs are distinct phenomena. PLEDs are resistant to treatment with antiepileptic drugs (AEDs).…”

A Hitchhiker's Guide to Functional Magnetic Resonance Imaging

“…Positron emission tomography (PET) and single-photon emission computerized tomography (SPECT) both have a long history of providing fundamental information regarding brain metabolism. Though lacking the time resolution of fMRI, they complement that methodology by having the ability to study such parameters as neurotransmitter-receptor interactions and local glucose metabolism for longer periods in time (minutes) (Price, 2012; Sander et al, 2013; Tousseyn et al, 2015). It is possible to perform fMRI and functional near-infrared spectroscopy (fNIRS) simultaneously, and such a multimodal approach may be used to improve the temporal resolution of the former, thus allowing better correlation of the BOLD signal with local hemodynamic changes (Steinbrink et al, 2006; Sato et al, 2013).…”