Frequency of Bitemporal Independent Interictal Epileptiform Discharges in Temporal Lobe Epilepsy

Abstract

Summary:Purpose: Bitemporal interictal epileptiform discharges (IEDs) occur in 542% of scalp EEGs in patients with temporal lobe epilepsy (TLE) studied with routine EEGs or partial analysis of long-term recordings.Methods: 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.Results: 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.Conclusions: 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.

Bitemporal epilepsy: A specific anatomo-electro-clinical phenotype in the temporal lobe epilepsy spectrum

“…3). These abnormalities (especially bilateral asynchronous IEDs) have been previously reported in other studies of BTLE, [11,18] but have also been described in some UTLE patients, [19] in whom their significance for post-surgical outcomes has not yet been clarified [9,18,20,21]. Consequently, they cannot be considered sufficient to distinguish the two groups of patients.…”

Hypersexuality after Temporal Lobe Resection

“…Bilateral hippocampal sclerosis is frequently observed postmortem (31,32). Bitemporal interictal epileptiform discharges are also frequently observed on scalp EEG (33), and bitemporal seizure onset occurs in 13% of TLE patients studied with depth EEG (30,34). The volume of the amygdala or hippocampus is abnormal bilaterally in 28% of patients with TLE (35) and the figure is even higher when there is a history of encephalitis or meningitis (36).…”

Factors Contributing to Clinical Seizure Lateralization in Patients with Mesial Temporal Lobe Epilepsy

“…Studies comparing the effects of unilateral and bilateral IEDs on postoperative seizure outcome have also reported conflicting results. While several studies have shown positive results for the unilaterality of IEDs, others have shown no differences [22,23,24,25,26]. Independent bilateral IEDs, ictal asynchrony, switch of lateralized ictal activity and bilateral independent seizure activity are probably all indicators of bilateral independent excitability that lie along a continuum [12].…”