Ictal Onset and Spreading of Seizures of Parietal Lobe Origin

Intracerebral Correlates of Scalp EEG Ictal Discharges Based on Simultaneous Stereo-EEG Recordings

BACKGROUND AND OBJECTIVES

It remains unknown to what extent ictal scalp EEG can accurately predict the localization of the intracerebral seizure onset in presurgical evaluation of drug-resistant epilepsies. In this study, we aimed to define homogeneous ictal scalp EEG profiles (based on their first ictal abnormality) and assess their localizing value using simultaneously recorded scalp EEG and stereo-EEG.

METHODS

We retrospectively included consecutive patients with drug-resistant focal epilepsy who had simultaneous stereo-EEG and scalp EEG recordings of at least 1 seizure in the epileptology unit in Nancy, France. We analyzed 1 seizure per patient and used hierarchical cluster analysis to group similar seizure profiles on scalp EEG and then performed a descriptive analysis of their intracerebral correlates.

RESULTS

We enrolled 129 patients in this study. The hierarchical cluster analysis showed 6 profiles on scalp EEG first modification. None were specific to a single intracerebral localization. The "normal EEG" and "blurred EEG" clusters (early muscle artifacts) comprised only 5 patients each and corresponded to no preferential intracerebral localization. The "temporal discharge" cluster (n = 46) was characterized by theta or delta discharges on ipsilateral anterior temporal scalp electrodes and corresponded to a preferential mesial temporal intracerebral localization. The "posterior discharge" cluster (n = 42) was characterized by posterior ipsilateral or contralateral rhythmic alpha discharges or slow waves on scalp and corresponded to a preferential temporal localization. However, this profile was the statistically most frequent scalp EEG correlate of occipital and parietal seizures. The "diffuse suppression" cluster (n = 9) was characterized by a bilateral and diffuse background activity suppression on scalp and corresponded to mesial, and particularly insulo-opercular, localization. Finally, the "frontal discharge" cluster (n = 22) was characterized by bilateral frontal rhythmic fast activity or preictal spike on scalp and corresponded to preferential ventrodorsal frontal intracerebral localizations.

DISCUSSION

The hierarchical cluster analysis identified 6 seizure profiles regarding the first abnormality on scalp EEG. None of them were specific of a single intracerebral localization. Nevertheless, the strong relationships between the "temporal," "frontal," "diffuse suppression," and "posterior" profiles and intracerebral discharge localizations may contribute to hierarchize hypotheses derived from ictal scalp EEG analysis regarding intracerebral seizure onset.

The Temporal Lobe as a Symptomatogenic Zone in Medial Parietal Lobe Epilepsy

Some surgical failures after temporal lobe epilepsy surgery may be due to the presence of an extratemporal epileptogenic zone. Of particular interest is the medial parietal lobe due to its robust connectivity with mesial temporal structures. Seizures in that area may be clinically silent before propagating to the symptomatogenic temporal lobe. In this paper, we present an overview of the anatomical connectivity, semiology, radiology, electroencephalography, neuropsychology, and outcomes in medial parietal lobe epilepsy. We also present two illustrative cases of seizures originating from the precuneus and the posterior cingulate cortex. We conclude that the medial parietal lobe should be strongly considered for sampling by intracranial electrodes in individuals with nonlesional temporal lobe epilepsy, especially if scrutinizing the presurgical data produces discordant findings.

Functional surgery in pediatric drug-resistant posterior cortex epilepsy: Electro-clinical findings, cognitive and seizure outcome

PURPOSE

Epilepsies originated from the occipital, parietal and/or the posterior edge of the temporal lobe are grouped together into posterior cortex epilepsy (PCE). Our objective was firstly to describe electro-clinical and imaging findings in the presurgical evaluation of children with PCE, and secondly to identify potential factors associated with surgical and cognitive outcomes.

METHOD

From the total of patients referred to the Epilepsy Monitoring Unit of 'Hospital Universitario Niño Jesús' from 2003 to 2016, 55 had drug-resistant PCE. Different variables obtained from the multimodal presurgical work-up were analyzed among patients achieving seizure freedom after surgery (ILAE class 1) and patients with persistent seizures. Categorical variables were compared with Fisheŕs exact test and numeric variables with t-Student for independent samples, and multiple logistic regression were used to analyze predictive values.

RESULTS

Median duration of epilepsy until surgery was 5 years [3-10 years]. Fifty patients showed lesions in the MRI, and 62.5% had concordant MRI-PET corregistration. 37 (67%) patients were operated (lesionectomy in 21 subjects, tailored resection based on intracranial studies in 16), and 23 (62,2%) reached ILAE class 1, with a mean follow-up period of 3.51 [1-12] years. A lower number of basal seizures and antiepileptic drugs, a well-defined lesion on the MRI, an epileptogenic zone (EZ) restricted to the posterior quadrant and the normalization of postsurgical EEGs were associated with seizure freedom (p<0.05). Additionally, 65% of patients had a long-term improvement of cognitive performances.

CONCLUSIONS

Epilepsy surgery should be considered in children with drug-resistant PCE, especially in those with a restricted EZ.

'Tickling' seizures originating in the left frontoparietal region

We report a 10-year-old boy with mild developmental delay and epilepsy with new events of right back tickling and emotional upset. These initially appeared behavioral, causing postulation of habit behaviors or psychogenic nonepileptic seizures. Several ictal and interictal EEGs were unrevealing. Continuous EEG revealed only poorly localized frontal ictal activity. Given that his clinical symptoms suggested a parietal localization, double-density EEG electrodes were placed to better localize the epileptogenic and symptomatogenic zones. These revealed evolution of left greater than right frontoparietal discharges consistent with seizures at the time of the attacks. Medical management has significantly reduced the patient's seizures.

Persistent genital arousal disorder associated with functional hyperconnectivity of an epileptic focus

Persistent Genital Arousal Disorder (PGAD) refers to the experience of persistent sensations of genital arousal that are felt to be unprovoked, intrusive and unrelieved by one or several orgasms. It is often mistaken for hypersexuality since PGAD often results in a high frequency of sexual behaviour. At present little is known with certainty about the etiology of this condition. We described a woman with typical PGAD symptoms and orgasmic seizures that we found to be related to a specific epileptic focus. We performed a EEG/MEG and fMRI spontaneous activity study during genital arousal symptoms and after the chronic administration of 300 mg/day of topiramate. From MEG data an epileptic focus was localized in the left posterior insular gyrus (LPIG). FMRI data evidenced that sexual excitation symptoms with PGAD could be correlated with an increased functional connectivity (FC) between different brain areas: LPIG (epileptic focus), left middle frontal gyrus, left inferior and superior temporal gyrus and left inferior parietal lobe. The reduction of the FC observed after antiepileptic therapy was more marked in the left than in the right hemisphere in agreement with the lateralization identified by MEG results. Treatment completely abolished PGAD symptoms and functional hyperconnectivity. The functional hyperconnectivity found in the neuronal network including the epileptic focus could suggest a possible central mechanism for PGAD.