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Introcduction: The majority of patients suffering from temporal lobe epilepsy (TLE) due to hippocampal sclerosis usually demonstrate chronic disorder despite extensive drug therapy. For these patients, a surgical procedure often presents a viable therapeutical option. However, this requires extensive preoperative staging including neuroimaging, video EEG monitoring as well as neuropsychological testing. In order to evaluate language lateralization, the Wada-procedure is used as well as functional transcranial Doppler sonography. These diagnostic procedures aim at localizing the epileptogenic zone and functionally important cortical areas in order to estimate the possible risk of post-operative language and memory deficits. To date, no single parameter has been identified which is suited to predict the post-operative memory outcome. The aim of this study was therefore to evaluate possible parameters (using the aforementioned tests) in patients suffering from TLE and undergoing surgery to predict the post-operative memory outcome.
Methods: This study is a retrospective evaluation of data from patients who presented at the Department of Epilepsy at the University hospital of Marburg for video EEG monitoring. Patients suffering from temporal lobe epilepsy, who had undergone epilepsy surgery were included if the entire preoperative test data (Wada-test, functional transcranial Doppler sonography, neuropsychiatric monitoring) were available. Patients suffering from malignant tumors, extratemporal epilepsy and patients with incomplete data were excluded. Among the data collected, neuropsychiatric tests that display proper function of the temporal lobes (VLMT, HAWIE-R, ROCFT) were included. In addition, surgical resection measures as well as a depression score were used. With respect to functional transcranial Doppler sonography, we used the following parameters: lateralization index, standard error and latency of the lateralization index and maximal rate of change of cerebral blood flow after 10 to18 s (both on the right and left side). In order to test for correlations, Pearson’s product moment correlation was employed. In addition, t-Tests for unrelated variables were applied. Multiple testing was corrected for by adapting the p-value: variables were considered significant, if p<0.01.
Results: We included 36 patients (17 females) with a mean age of 37.5±12.1. This total group was divided into a subgroup consisting of patients with left sided (N=25) and patients with right sided TLE (N=11). 26 patients (72.2%) did not report any seizures one year postoperatively. In both groups of patients, the preoperative retention loss after verbal interference correlated significantly with the postoperative decline of this parameter (left: r=-0.740; p=0.000; N=18; right: r=-0.911; p=0.002; N=8). Depression scores in both groups were correlated between pre- and postoperative testing (left: r=-0.873; p=0.000; N=12; right: r=-0.801; p=0.017; N=8). Patients with left-sided TLE showed a tendency of a correlation between the maximum rate of change of flow in the right arteria cerebri media (when activated during Doppler sonography) and the postoperative changes of recall (r=0.931; p=0.021; N=5). Memory performance of the right hemisphere as measured during the Wada-test correlated well with the postoperative changes in retention loss after verbal interference (r=-0.577; p=0.016; N=18). Finally, in patients with left sided disease, the results of language lateralization between Wada testing and functional transcranial Doppler sonography showed a strong correlation (r=-0.638; p=0.003; N=19). For patients with right sided epilepsy, no correlations were detected, most likely due to the low size of the group.
Discussion: We were able to demonstrate a clear correlation of language lateralization when comparing the results obtained in Wada procedure and functional transcranial Doppler sonography, which is in line with previous results from the literature. We therefore suggest that functional transcranial Doppler sonography is sufficiently proven as an alternative method to the Wada procedure. In addition, in both patient groups good preoperative retention performances are associated with a greater loss postoperatively. For patients with left sided TLE, the rate of change of flow in the right arteria cerebri media seems to be suited to predict the postoperative outcome. Finally, the association between the contralateral memory performance in the Wada test and postoperative changes in retention loss after verbal interference are a suitable parameter. We therefore hypothesize that a combination of neuropsychiatric testing and functional transcranial Doppler sonography (if necessary in combination with the Wada-procedure) can be used to predict postoperative memory outcome in patients with left sided TLE undergoing surgery. However, these parameters need further evaluation in prospective studies.