Focal epilepsy

see also Subclinical focal seizure.

Focal seizures (also called partial seizures and localized seizures) are seizures which affect initially only one hemisphere of the brain.

In partial seizures the seizure is generated in and affects just one part of the brain – the whole hemisphere or part of a lobe. Symptoms will vary according to where the seizure occurs. In the frontal lobe symptoms may include a wave-like sensation in the head; in the temporal lobe, a feeling of déjà vu; in the parietal lobe, a numbness or tingling; and in the occipital lobe, visual disturbance or hallucination.

Mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) is the most common type of focal epilepsy.

Limb shaking transient ischemic attack is a rare manifestation of Steno-occlusive carotid artery disease. The symptoms usually point towards a seizure like activity and misdiagnosed as focal seizures.

Focal epilepsies are caused by a malfunction of nerve cells localised in one part of one cerebral hemisphere. In studies, estimates of the number of individuals with focal epilepsy who do not become seizure-free despite optimal drug therapy vary according to the age of the participants and which focal epilepsies are included, but have been reported as at least 20% and in some studies up to 70%. If the epileptogenic zone can be located surgical resection offers the chance of a cure with a corresponding increase in quality of life.

Kokkinos et al. identified 51 focal epilepsy patients implanted with a minimum of two electrodes - unilateral anterior and posterior - in either hippocampus. We used visual inspection of the intracranial electroencephalogram (iEEG) and 3D brain volume spectrum-based statistical parametric mapping (SPM) to localize barques.

In 18/51 patients (35.29%), barques were identified in 22/70 (31.42%) hippocampi. In all hippocampi (100%), barques were present in the posterior hippocampus, while 9 (40.90%) showed concurrent non-independent barque activity anteriorly (P < 0.0001). Statistical parametric mapping confirmed the posterior barque localization, with significant differences in t-values (t(27) = 8.08, P < 0.0001) and z-scores (t(24) = 6.85, P < 0.0001) between anterior and posterior hippocampal barque activity. Posterior lateral extrahippocampal contacts demonstrated phase reversals of positive polarity during barque activity (P = 0.0092, compared to anterior extrahippocampal contacts).

Conclusions: This study highlights the posterior hippocampal predominance of barques. Our findings are concordant with the posterior distribution of the scalp manifestation of barques as “14&6/sec positive spikes”. The posterio-lateral hippocampal barque phase reversal can explain the positive polarity of scalp 14&6/sec spikes.

Significance: Understanding the properties of barques is critical for the iEEG interpretation in epilepsy surgery evaluations that include the hippocampus 1).

Long-term EEG, recorded with the standard 25-electrode array of the IFCN, from 41 consecutive patients with focal epilepsy who underwent resective surgery, were analyzed blinded to the surgical outcome. The automated analysis comprised spike-detection, clustering and source imaging at the half-rising time and at the peak of each spike-cluster, using individual head-models with six tissue-layers and a distributed source model (sLORETA). The fully automated approach presented ESI of the cluster with the highest number of spikes, at the half-rising time. In addition, a physician involved in the presurgical evaluation of the patients, evaluated the automated ESI results (up to four clusters per patient) in clinical context and selected the dominant cluster and the analysis time-point (semi-automated approach). The reference standard was location of the resected area and outcome one year after operation.

Accuracy was 61% (95% CI: 45-76%) for the fully automated approach and 78% (95% CI: 62-89%) for the semi-automated approach.

Automated ESI has an accuracy similar to previously reported neuroimaging methods.

Automated ESI will contribute to increased utilization of source imaging in the presurgical evaluation of patients with epilepsy 2).

Forty patients with focal epilepsy who underwent presurgical stereo-electroencephalography (SEEG) were included in the study. SEEG data have been recorded with sampling rate of 25 kHz and 30 minutes of resting period was analyzed for each patient. Ten patients met selected criteria for analyses of correlations with surgical outcome - detection of interictal ripples (R), fast ripples (FR) and VHFOs, resective surgery, and at least one-year post-operative follow-up. Using power envelope computation and visual inspection of power distribution matrixes, electrode contacts with high-frequency oscillations (HFOs) and very high frequency oscillations (VHFOs) were detected and analyzed.

Interictal very fast ripples (VFR; 500-1000 Hz) were detected in 23 out of 40 patients and ultra fast ripples (UFR; 1000-2000 Hz) in almost half of investigated subjects (N=19). VFR and UFR were observed only in patients with temporal lobe epilepsy and were recorded exclusively from mesiotemporal structures. The UFR were more spatially restricted in the brain then lower frequency HFOs. When compared to R oscillations, significantly better outcomes were observed in patients with higher percentage of removed contacts containing FR, VFR, and UFR.

Interictal VHFOs are relatively frequent abnormal phenomena in patients with epilepsy, and appear to be more specific biomarkers for epileptogenic zone when compared to traditional HFOs 3).

Kokkinos V, Urban A, Frauscher B, Simon M, Hussein H, Bush A, Williams Z, Bagić AI, Mark Richardson R. Barques are generated in posterior hippocampus and phase reverse over lateral posterior hippocampal surface. Clin Neurophysiol. 2022 Feb 4;136:150-157. doi: 10.1016/j.clinph.2022.01.132. Epub ahead of print. PMID: 35168029.
Baroumand AG, van Mierlo P, Strobbe G, Pinborg LH, Fabricius M, Rubboli G, Leffers AM, Uldall P, Jespersen B, Brennum J, Henriksen OM, Beniczky S. Automated EEG source imaging: A retrospective, blinded clinical validation study. Clin Neurophysiol. 2018 Sep 24;129(11):2403-2410. doi: 10.1016/j.clinph.2018.09.015. [Epub ahead of print] PubMed PMID: 30278389.
Brázdil M, Pail M, Halámek J, Plešinger F, Cimbálník J, Roman R, Klimeš P, Daniel P, Chrastina J, Brichtová E, Rektor I, Worrell GA, Jurák P. Very high frequency oscillations: Novel biomarkers of the epileptogenic zone. Ann Neurol. 2017 Aug 5. doi: 10.1002/ana.25006. [Epub ahead of print] PubMed PMID: 28779553.
  • focal_epilepsy.txt
  • Last modified: 2022/08/02 19:03
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