Abstracts

The purpose of this cross-sectional investigation was to: a) characterize the nature and extent of cognitive morbidity in chronic temporal lobe epilepsy (TLE), b) determine whether cognitive morbidity progresses in association with increasing years of epilepsy, and c) identify factors that may accelerate or slow progressive cognitive effects.
Healthy controls (n = 85) and patients with TLE (n = 96), ranging in age from 14 to 60 years, underwent comprehensive neuropsychological assessment of intelligence, language, perception, verbal and nonverbal memory, psychomotor processing, and speeded fine motor dexterity. Twenty cognitive indices were derived for each subject from this test battery. Test scores were converted to adjusted (age, gender, education) z-scores and an impairment index computed for each subject, defined as the proportion of test scores exceeding z = -1.5.
Three sets of findings were evident: 1) Chronic TLE was associated with widespread cognitive morbidity. At the group level, TLE patients exhibited significantly poorer performance across all cognitive domains compared to controls, with several cognitive abilities (motor speed, mental flexibility, naming) at least as impaired as memory function. At the individual subject level, an average of 37% of test scores were abnormal per TLE patient compared to 7.8% for controls (p [lt] 0.001). 2) Evidence of cognitive progression was obtained. Increasing duration of epilepsy was significantly associated with a larger proportion of abnormal test scores per patient (r = .40, p [lt] 0.001). This relationship remained significant after controlling for several factors (e.g., polytherapy, seizure frequency and other clinical seizure features). 3) There are factors that appear to attenuate the adverse effects of chronic epilepsy on cognition. Among patients with greater cerebral reserve (defined as 12+ years of education), the adverse effects of increasing duration of epilepsy on cognition were significantly attenuated (r = .19, ns) compared to that observed among patients with less cerebral reserve (r = .53, p [lt] 0.001).
These findings provide a greater understanding of the nature and extent of cognitive morbidity associated with chronic TLE. Cognitive morbidity can be widespread, affect several cognitive domains at least as severely as memory, with an average of 37% of test scores abnormal per individual TLE patient. Cognitive morbidity increases with the chronicity of epilepsy and, consistent with human and animal findings, factors were identified that appear to attenuate the degree of associated cognitive morbidity.
[Supported by: NIH 2RO1-37738 and MO1 03186]