Temporal Interictal Epileptiform Discharges Research Articles

The Role of Scalp EEG in the Presurgical Evaluation of Patients with Medically Refractory Temporal Lobe Epilepsy

ABSTRACT.Although the scalp EEG findings in medically refractory temporal lobe epilepsy (TLE) have been known for more than half a century, recent developments have helped us to utilize these data more effectively in selecting ideal candidates for epilepsy surgery and thereby improving the postoperative seizure outcome. We have summarized the currently available information about the value and limitations of interictal and ictal scalp EEG data in the localization of the epileptogenic focus. A majority of patients with medically refractory TLE can be recruited for surgery based on concordant scalp EEG and magnetic resonance imaging findings. There are distinctive characteristics in the interictal and ictal scalp EEG that, when correlated with clinical, neuropsychological, and imaging data, are helpful in differentiating between mesiobasal and lateral (neocortical) TLE syndromes. Future research on the role of scalp EEG in the presurgical evaluation of patien ts with medically refractory TLE should concentrate on the following areas: influence of sleep on temporal interictal epileptiform discharges (IEDs) and its implications; frequency, pathogenesis, and significance of bilateral independent temporal IEDs; anatomopathological correlates of scalp-recorcled interictal and ictal EEG patterns; cost-effective utilization of long-term EEG-video monitoring by selecting the subjects who require this investigation; the role of sphenoidal electrodes in ascertaining interictal and ictal EEG data; the significance of scalp-recorded interhemispheric propagation of ictal rhythms and its prognostic implications; and the correlation of scalp-recorded EEG data with magnetoencephalography and functional neuroimaging findings.

The lateralizing and surgical prognostic value of a single 2-hour EEG in mesial TLE

We investigated 109 patients who received anterior temporal lobectomy for intractable mTLE by post-operative follow-up for at least 11/2 years. We reviewed pre-operative 2-hour interictal EEGs, counted interictal epileptiform discharges (IEDs), and compared the lateralization of IEDs with the side of surgery and surgical outcome. Twenty of 22 patients who had no spikes and 44 of 51 who had unitemporal spikes became seizure free after surgical resection. The correct lateralization of the epileptogenic side was possible in 90.9% of the patients with unitemporal IEDs. In 12 seizure-free patients of 15 patients with less than 70% predominance of IED in one temporal lobe, the positive predictive value of the lateralization was 41.7%. In 16 seizure-free patients of 21 with more than 70% preponderance of IED in one lobe, the positive predictive value was 81.3%. Surgical outcome of patients with unitemporal and bitemporal IEDs were not significantly different. Interictal scalp EEG can be used as a lateralizing tool in mTLE when the temporal IEDs appear with more than 70% preponderance in one side. Although the presence of bitemporal IEDs often causes confusion in terms of the correct lateralization, it does not affect the surgical outcome.

Frequency of bitemporal independent interictal epileptiform discharges in temporal lobe epilepsy.

Bitemporal interictal epileptiform discharges (IEDs) occur in < or =42% of scalp EEGs in patients with temporal lobe epilepsy (TLE) studied with routine EEGs or partial analysis of long-term recordings. Twenty-eight patients with TLE demonstrating exclusively unilateral temporal IEDs on routine EEGs underwent 24-h continuous recording. The entire record was visually inspected for epileptiform discharges. We used continuous EEG to assess the significance of long-term recording in detecting bilateral IEDs. Twenty-two patients had left temporal IEDs; 21 had right temporal IEDs. Seventeen (61%) patients had IEDs originating from both the right and left temporal lobes. The probability of detecting bilateral independent IEDs was correlated with the duration of continuous EEG recording. There was no correlation between the number of IEDs originating from one side and the probability of detecting independent IEDs on the other side. The frequencies of IEDs were not correlated with the length of time since onset of epilepsy. The findings suggest that when long-term recordings are performed, the incidence of bilateral discharges in TLE is higher than previously reported in the literature and supports the view that TLE is commonly a bilateral disease.

Lateralizing value of interictal spikes on overnight sleep-EEG studies in temporal lobe epilepsy.

To determine the lateralizing value of interictal epileptiform discharges (IEDs) recorded during overnight sleep-EEG studies in temporal lobe epilepsy. Because IEDs are more prevalent in non-rapid eye movement (NREM) sleep than in wakefulness, overnight sleep-EEG recordings may contribute additional lateralizing information to the epilepsy surgery evaluation beyond daytime EEGs. Twenty-four subjects with medically refractory temporal lobe epilepsy underwent continuous overnight sleep-EEG recordings. Subjects were seizure free > or =24 h before study and receiving stable doses of medication. The IED foci recorded on overnight studies were compared with daytime EEGs, interictal samples, and ictal recordings during long-term monitoring, brain magnetic resonance images (MRIs), and surgical outcome. (a) In all 24 subjects, including 13 without IEDs on daytime EEGs, temporal IEDs were present during NREM sleep and were exclusively or predominantly (>95%) unilateral in 15 and bitemporal in nine. (b) Unilateral NREM IEDs were concordant with surface or depth ictal-onset regions in 14 subjects, even if MRIs were normal (three subjects) or surface ictal-onset regions were bilateral (five subjects). Eleven of 12 subjects with unilateral concordant NREM IEDs who have undergone surgery are seizure free. (c) Bitemporal IEDs were associated with postoperative seizures in all subjects with normal MRIs or widespread MRI abnormalities. However, all subjects with bitemporal IEDs and MRI hippocampal abnormalities concordant with ictal-onset regions had good to excellent surgical outcomes. When combined with other investigations, IEDs recorded on overnight studies add prognostic data to the epilepsy surgery evaluation not provided by daytime EEGs.

Familial temporal lobe epilepsy: a common disorder identified in twins.

We describe a new syndrome of familial temporal lobe epilepsy in 38 individuals from 13 unrelated white families. The disorder was first identified in 5 concordant monozygotic twin pairs as part of a large-scale twin study of epilepsy. When idiopathic partial epilepsy syndromes were excluded, the 5 pairs accounted for 23% of monozygotic pairs with partial epilepsies, and 38% of monozygotic pairs with partial epilepsy and no known etiology. Seizure onset for twin and nontwin subjects usually occurred during adolescence or early adult life. Seizure types were simple partial seizures with psychic or autonomic symptoms, infrequent complex partial seizures, and rare secondarily generalized seizures. Electroencephalograms revealed sparse focal temporal interictal epileptiform discharges in 22% of subjects. Magnetic resonance images appeared normal. Nine affected family members (24%) had not been diagnosed prior to the study. Pedigree analysis suggested autosomal dominant inheritance with age-dependent penetrance. The estimated segregation ratio was 0.3, indicating an overall penetrance of 60% assuming autosomal dominant inheritance. The mild and often subtle nature of the symptoms in some family members may account for lack of prior recognition of this common familial partial epilepsy. This disorder has similarities to the El mouse, a genetic model of temporal lobe epilepsy with a major gene on mouse chromosome 9, which is homologous with a region on human chromosome 3.