Repeated Intracarotid Amobarbital Tests

Abstract

To the Editors: We read with interest the article titled “Repeated Intracarotid Amobarbital Tests” by Tobias Loddenkemper and colleagues published in the March issue of Epilepsia. Given the dearth of published data regarding repeated IAT, we applaud Dr. Loddenkemper and his colleagues for pursuing this topic, but we also find it necessary to address one conclusion regarding their findings. Briefly, Dr. Loddenkemper and his colleagues examined retrospective data from their center to determine the frequency of repeat IAT, the reasons for IAT retesting, and the test–retest reliability of IAT for language and memory functioning. They found that the vast majority of IAT procedures were repeated due to obtundation and inability to test for memory or language lateralization (i.e., 90%). Lateralization of language functions as assessed by relative length of speech arrest was robust following retest whereas lateralized memory performance was “contradictory” in the majority of cases. They concluded, “… lateralization with the IAT may be varying and unreliable in patients who failed the first test,” and they recommended abandoning repeated Wada testing as well as any Wada testing in uncomplicated temporal lobe epilepsy surgical patients. While the authors' statement is technically true (i.e., the majority of repeated IAT procedures produced different memory results), it is misleading because it implies that the IAT memory test itself lacks reliability. Rather, the majority of IAT procedures were repeated because the initial trial was invalid due to factors such as obtundation or lack of hemiparesis. It is inappropriate to discuss test–retest reliability when one trial was, by definition, invalid. The fact that lateralization of speech arrest did not change despite the invalidity of the first trial is not surprising given the neuroanatomy of speech production and the ease of assessing for the presence or absence of speech following hemispheric deactivation using sodium amobarbital. Unfortunately, memory testing requires the sustained attention and participation of the patient for over 1 minute while memory stimuli are presented, and reactions to the various medications used in the Wada test can vary unpredictably. A “contradictory” score on IAT retest can very easily reflect a good trial versus an invalid one. The reliability of the IAT memory test can only be assessed reliably by comparing two valid trials. To suggest a policy of not repeating Wada tests based on these findings strikes us as imprudent, particularly given the relatively recent introduction of Brevital as an alternative sedative that allows for retesting without recatheterization, thus minimizing the risks of repeat testing.