Temporal Lobe Spikes Affect Distant Intrinsic Connectivity Networks

Abstract

Objective: To evaluate local and distant blood oxygen level dependent (BOLD) signal changes related to interictal epileptiform discharges (IED) in drug-resistant temporal lobe epilepsy (TLE).Methods: Thirty-three TLE patients undergoing EEG–functional Magnetic Resonance Imaging (fMRI) as part of the presurgical workup were consecutively enrolled. First, a single-subject spike-related analysis was performed: (a) to verify the BOLD concordance with the presumed Epileptogenic Zone (EZ); and (b) to investigate the Intrinsic Connectivity Networks (ICN) involvement. Then, a group analysis was performed to search for common BOLD changes in TLE.Results: Interictal epileptiform discharges were recorded in 25 patients and in 19 (58%), a BOLD response was obtained at the single-subject level. In 42% of the cases, BOLD changes were observed in the temporal lobe, although only one patient had a pure concordant finding, with a single fMRI cluster overlapping (and limited to) the EZ identified by anatomo-electro-clinical correlations. In the remaining 58% of the cases, BOLD responses were localized outside the temporal lobe and the presumed EZ. In every patient, with a spike-related fMRI map, at least one ICN appeared to be involved. Four main ICNs were preferentially involved, namely, motor, visual, auditory/motor speech, and the default mode network. At the single-subject level, EEG–fMRI proved to have high specificity (above 65%) in detecting engagement of an ICN and the corresponding ictal/postictal symptom, and good positive predictive value (above 67%) in all networks except the visual one. Finally, in the group analysis of BOLD changes related to IED revealed common activations at the right precentral gyrus, supplementary motor area, and middle cingulate gyrus.Significance: Interictal temporal spikes affect several distant extra-temporal areas, and specifically the motor/premotor cortex. EEG–fMRI in patients with TLE eligible for surgery is recommended not for strictly localizing purposes rather it might be useful to investigate ICNs alterations at the single-subject level.

Delayed effective connectivity characterizes the epileptogenic zone during stereo-EEG

“…Interictal epileptiform discharges (IEDs) may interrupt the usual local and remote neuronal propagation (Mirandola et al, 2021), although decreased connectivity in the EZ has been described in the absence of interictal spikes (Coito et al, 2016). In contrast, abnormal connections arising from epileptic networks occur in the absence of interictal spikes and are reinforced by their presence (Iannotti et al, 2016).…”

Epileptogénesis y corteza piriforme: entendiendo a la epilepsia del lóbulo temporal más allá del hipocampo

“…Su ubicación anatómica estratégica permite que sea una vía común para la propagación de descargas epileptiformes en las epilepsias focales. Esto se correlaciona con algunos estudios de neuroimagen los cuales han demostrado que, en pacientes con epilepsia del lóbulo temporal, la disfunción de los circuitos anatómicos va más allá del hipocampo y afecta a muchas otras estructuras (24)(25)(26). Estos estudios han identificado cambios volumétricos y morfológicos en la CPR, lo que sugiere que su atrofia es ipsilateral al foco epiléptico.…”

Electroencephalography–functional magnetic resonance imaging for clinical evaluation in focal epilepsy

“…One study reported the accuracy of EEG‐fMRI in localizing the seizure‐onset zone (SOZ) with stereo‐EEG (SEEG) and found that 77% of patients had at least one study with primary EEG‐fMRI clusters concordant with an SEEG‐defined SOZ 15 . Another study claimed that the spike‐related BOLD response represented intrinsic connectivity networks 16 . Several studies have proposed routine clinical use of EEG‐fMRI in the pre‐surgical evaluation of medically refractory epilepsy patients 17–21 .…”

“… 15 Another study claimed that the spike‐related BOLD response represented intrinsic connectivity networks. 16 Several studies have proposed routine clinical use of EEG‐fMRI in the pre‐surgical evaluation of medically refractory epilepsy patients. 17 , 18 , 19 , 20 , 21 However, these reports did not assess the added value of EEG‐fMRI in a standard clinical evaluation.…”