Rationale:
In patients with temporal lobe epilepsy, determination of dominant hemisphere for language and memory is critical for pre-surgical evaluation. Wada test (WT) and neuropsychology (NP) assessment are utilized measures to predict potential memory decline post-operatively.
Interictal discharges or seizures induced by Methotexital (MHT) have been widely reported (Kirchberger et al. 1998, Fiol et al. 1990), although there is scarce data on their influence on working memory during WT, potentially altering results (Danoun et al. 2021). We present a case with highly preserved verbal memory on NP evaluation who had MHT induced Lateralized Periodic Discharges (LPDs) on the language dominant side resulting in a significant decrease in memory performance below the expectation based on pre-test NP evaluation.
Methods:
WT to lateralize language and memory was performed: 7 mg of Sodium MHT was injected in the left and right carotid arteries, respectively. Angiograms revealed no contralateral blood flow during dye injection. Approximately 30 min elapsed between the injections. Language was assessed by testing fluency and naming during the anesthetized state. Memory was assessed by testing spontaneous recall and cued object recognition of the words and pictures shown during and after the anesthetized state. We compared the results of pre-test NP verbal memory scores, using Wechsler Memory Scale (M: 100, SD: 15 in normative sample) and WT recall scores.
Results:
Our patient is a 29-year-old right-handed woman with left temporal lobe epilepsy since age five. NP assessment showed no significant difference between verbal and visual memory with both being above average (Figure 1a).
Baseline EEG showed no interictal activity before the injections (Figure 2a). After the initial injection into the left internal carotid artery (Figure 2b), LPDs at left frontal region were observed approximately 16 sec later, during the presentation of memory items (Figure 2c,d). These lasted 77 seconds. WT confirmed left lateralization of language function (Figure 1b). Results of WADA are shown in Figure 1b.
Conclusions:
Although no interictal discharges were observed before the injections, they appeared right after each injection, simultaneously with the arm drop in each side, making a coincidental association highly unlikely. This is in concordance with the previous findings showing Methotexital’s effect of inducing spikes in areas that no interictals were observed before in addition to the same location of previous interictals (Fiol et al. 1990).
Our patient’s memory performance during the assessment of the language dominant hemisphere was below the expectation based on pre-test NP evaluation. We believe this is likely due to frequent LPDs seen in the frontal lobe during the first injection producing a state of exhaustion (“post-ictal state”), affecting working memory performance while the left hemisphere was being assessed during the second part of the test.
In conclusion, caution should be taken while interpreting Wada memory results in the presence of LPDs. Our findings also supports the hypothesis of interictal epileptiform discharges causing cognitive dysfunction (Danoun et al. 2021).
Funding: No funding was received.