Abstracts

Language and memory preferentially develop in the same hemisphere; thus, verbal memory impairment is typically associated with left medial temporal lobe dysfunction while non-verbal memory impairment suggests a right hemisphere focus. However, in patients with left mesial temporal lobe epilepsy, this association may not be well established. Occasionally patients with a clear left hippocampus seizure focus and an apparently normal right hippocampus fail the Wada test with left side injection. We hypothesized that in left mesial temporal lobe epilepsy, a late age of onset may account for these unpredicted Wada failures. Specifically, we reasoned that during the critical years when language develops and becomes established in the left hemisphere, strong connections with the left hippocampus are formed preferentially; in early onset left temporal lobe epilepsy, connections are strengthened with the right hippocampus when the left is dysfunctional. After the critical period of language development (generally accepted as [le] 7 years old), we hypothesized that connections from left hemisphere language cortex to right medial temporal lobe would be more difficult to establish, and this connection is necessary for verbal encoding of non-verbal items. Therefore, in patients with late onset ([ge] 8 years old) left mesial temporal lobe epilepsy, we predicted that the right hippocampus may not be able to support memory after the left hippocampus loses its function secondary to longstanding seizures. To test this hypothesis we studied the relationship between left hemisphere Wada failures and age of seizure onset., We reviewed data on 69 patients who were admitted for pre-surgical evaluations for mesial temporal lobe epilepsy. Wada tests were performed as part of the pre-surgical evaluation. Forty-two patients had left mesial temporal lobe epilepsy and 27 patients had right mesial temporal lobe epilepsy., Of the 42 left mesial temporal lobe epilepsy, 18 had an early onset ([le] 7 years old) and 24 had a late onset ([ge] 8 years old). All 18 early onset patient passed the Wada test with left sided injection. Nineteen of the 24 late onset patient passed the Wada test and 5 of the 24 failed (less than 60 % recognition memory). The passing rate of the Wada test in early onset left mesial temporal lobe cases was significantly higher than the late onset group (p [lt] 0.05). In the right mesial temporal lobe epilepsy patients, there was no significant difference between the early and late onset groups (1 out of 10 in the early onset and 1 out of 17 in the late onset did not pass the Wada test)., Age of seizure onset may help to predict the Wada failure in left temporal lobe epilepsy. A greater incidence of Wada failures in late onset patients with left mesial temporal epilepsy compared to early onset patients suggests that memory laterality develops in concert with language development.,