Abstracts

RATIONALE: Because Wada evaluations are not standardized, it is impossible to know to what degree method variance accounts for reported differences in results. To address this deficiency, three comprehensive epilepsy surgery centers compared the type of memory stimuli used to predict side of seizure onset among children being considered for epilepsy surgery.
METHODS: One hundred and fifty-two children (mean age: 13.37 yrs., range 7 - 16 yrs.) with intractable epilepsy underwent Wada testing as part of their preoperative evaluation for possible epilepsy surgery. Seizure onset was determined by simultaneous video/EEG monitoring of multiple seizures. Wada memory asymmetries were evaluated using either: 1) real objects presented immediately after injection and assessed after return to baseline with no verbal response expected, or 2) verbal and nonverbal stimuli (e.g., printed words, arithmetic problems, photographs and line drawings) presented primarily on cards immediately after injection and assessed after return to baseline with verbal responses expected from the patient. Although slight institutional differences existed in procedures for amobarbital administration, there was no statistically significant difference between left (mean=100.66 mg) and right (mean=99.53 mg) hemisphere amobarbital doses.
RESULTS: When using real objects with no language confound, Wada memory asymmetries accurately predicted seizure laterality to a statistically significant degree
in both left and right seizure onset children (p = .0001). In contrast, Wada memory asymmetries using primarily verbally-oriented materials presented on cards were unable to predict seizure laterality among left seizure onset patients (p = .34), but successfully identified right seizure onset patients (p = .001). Identical, but more robust, results were obtained when the analysis included only children with temporal lobe epilepsy (N=88).
CONCLUSIONS: Results suggest the use of verbally-oriented memory stimuli (e.g., printed words, arithmetic problems, repetition of a nursery rhyme) diminishes the capacity of the Wada test to predict lateralized seizure onset in children with seizures originating in the left hemisphere. Furthermore, these results (in conjunction with previous findings) raise the possibility that using real objects as memory stimuli during the Wada procedure may be superior to using memory stimuli presented on cards for predicting side of seizure onset.