Abstracts

RATIONALE: The intracarotid amobarbital test (IAT) is the gold standard to determine language and memory lateralization in candidates for epilepsy surgery. A literature review revealed 5 series with a total of 87 cases of repeated IATs. Our goal was to determine the frequency of repeated IATs at our center, and to estimate the re-test reliability of the IAT for both language and memory lateralization.
METHODS: 1249 consecutive IATs on 1190 patients between 1989 and 2001 were reviewed. Test re-test interval, side of injection, time until first verbal response and memory scores were documented. All patients were separately catheterized for the retest procedure, and all tests were performed on separate days. Amobarbital dose was decreased in most of the repeated procedures. A memory test change outside the 95% confidence interval was considered significant. Correlations were calculated with Pearson[ssquote]s correlation coefficient.
RESULTS: 53 patients (4.4 %) underwent a second IAT and 3 patients (0.24%) had a third IAT. The charts of 3 patients were missing. Therefore 50 patients with 31 uni- and 19 bilateral repeated IATs were included (69 hemispheres , 45 left). Retest interval ranged from 1 to 1119 days (median 95.5 days). Reasons for repetition included obtundation and inability to test for memory lateralization (32), inability to test for language lateralization (13), no hemiparesis during first test (2), no aphasia during first test (1), atypical vessel filling (1) and bleeding complications from the catheter insertion site (1). Language lateralization was reproduced in all patients. Memory improved after left injection in 7 out of 45 patients and deteriorated in 1. After right sided injection 1 out of 24 patients improved and 2 deteriorated. Pearson[ssquote]s correlation coefficient between the first and second memory test was low (left r=0.147, right r=0.155). Bilateral repeated memory testing was available in 19 patients. In 2 patients memory dominance switched sides. Seven patients again showed bilateral memory representation, 5 patients went from bilateral memory representation to unilateral dominance and 5 patients with an initally lateralized memory showed bilateral memory on the second test.
CONCLUSIONS: In 4% of patients the IAT was repeated in order to deliver satisfactory information on either language or memory lateralization. Obtundation and inablility to test for memory or language were the usual reasons for repetition. Speech lateralization of the IAT was always reproduced. Repeated memory test results did not correlate as well and memory lateralization was unreliable in 63% of the patients. Memory improvement was more likely to occur with left than right-sided injection. Test results were limited by a varying dose of amobarbital, crossover of amobarbital from one side to the other, testing of both hemispheres on the same day, practice effects, unblinded observers, fluctuating cooperation of the patients and a biased sample of patients. Gain of reliable information versus the risks of complications and failed tests has to be considered when a patient is subjected to an IAT.
[Supported by: This work was supported by Innovative Medizinische Forschung, WWU Münster (FoeKz. LO 610101) and NRW-Nachwuchsgruppe Kn2000, Federal Ministry of Education and Research (Foe.1KS9604/0), Interdisciplinary Center of Clinical Research Münster (IZKF Project NWG2).]