Taking Sides: Physician's Perceptions on the Use of the Wada Test in Epilepsy Surgery—Q-PULSE Survey Commentary

Abstract

The recent Q-PULSE Survey compiled by Chad Carlson asked members to place the Wada test (bilateral intracarotid amobarbital test) in the context of the current practice of epilepsy surgery. Historically, the Wada test has three purposes: to lateralize language, to assess the risk of memory loss after epilepsy surgery, and to help provide predictive data in localization of the epileptic focus.

The Wada test, however, generates strong opinions. Like driving on the right or left side of the road, whether or how the Wada is used may depend on where one was raised. For example, respondents widely diverge on the frequency of use of the Wada test. About one-third of subjects use the Wada for “all or nearly all” surgery candidates; almost the same proportion cite the risk of the procedure as the main reason why it is avoided.

Regarding language, 56% of respondents use Wada for language lateralization for more than 50% of patients, compared with 37% who use fMRI and 8% who use MEG. Since these proportions were the same as for those who used these three procedures in general, language lateralization appears to come “free” with the study, and language lateralization is not really the source of disagreement.

The most divergent opinions centered on the latter two uses: postsurgical memory risk and prediction of outcome. Previous studies document that poor memory that is worse ipsilateral to the surgical target correlates with focal hippocampal pathology (1). Asymmetric, poor memory ipsilateral to the proposed surgical target helps confirm the hippocampus as the location of epileptic pathology when correlating with other measures of localization (2). Yet, clear lateralization of memory and predictions of amnesia following anterior temporal lobectomy don't follow Wada findings in lockstep. Furthermore, differences in Wada protocols and differences in what constitutes a “Wada failure” cloud the literature. Because of this lack of clarity, it's easy to see why our respondents ranked the functions of memory lateralization and prediction as first and last, respectively, as primary indications to perform a Wada test.

The conflict continues in what physicians choose to do with the information. For example, when asked what the next step would be if memory findings point the “wrong way” (poor residual memory mediated by the “normal” hippocampus when injecting the side of proposed surgery), physicians differ greatly on what to advise a patient. More than 15% advised pressing forward with surgery despite the potential of memory loss. The benefits of seizure remission, in their opinion, surpass any theoretical risks of worse postoperative memory. A near similar proportion (14%) advised the opposite; in their view, patients should decline surgery because the risk of severe memory loss is too great. A similar difference exists when findings of the Wada test, whether language or memory, disagree with neuro-psychologic testing. Whereas 30% would proceed with surgery recognizing increased risk, 26% would advise against surgery.

These different viewpoints, just as drive-on-the-right rules, are difficult to reconcile. Perhaps the survey design pushed physicians into this split. After all, risks vary. Since 30–60% of patients who undergo dominant anterior temporal lobectomy will experience significant verbal memory impairment, and that the severity of deficit depends on the baseline impairment (3), the survey does not evaluate the calculus that each physician brings to individual cases in using or evaluating the Wada test.

Technology may provide a way out. Just as the autonomous car may prove helpful in reducing driving errors, advances in noninvasive imaging (in particular, fMRI) may help improve the risk–benefit analysis of epilepsy surgery. In the case of lateralization of language, fMRI appears to correlate tightly with the Wada test (4). Although the Wada test remains the gold standard in memory lateralization, a recent publication (5) provides evidence that a thoughtful protocol in fMRI acquisition can provide useful information about memory function without the perceived risks inherent in invasive procedures. With future work, perhaps epileptologists will feel more comfortable driving in the same lane.