Abstracts

No study has been published on the cognitive correlates of temporal lobe abnormality as determined by ¹¹C-flumazenil (FMZ) positron emission tomography (PET). The use of FMZ PET is helpful in localizing temporal lobe seizure onset because of decreased central benzodiazepine receptor density in the region of epileptogenic zone. The objective of this study was to evaluate cognitive performance in patients demonstrating temporal lobe FMZ PET abnormality in isolation and in the presence of MRI-defined lesions, including mesial temporal sclerosis. It is hypothesized that those patients demonstrating both structural and functional abnormality will perform worse on neuropsychological (NP) measures as compared to patients showing only functional temporal lobe dysfunction.
The sample was eight patients who underwent FMZ PET as part of a presurgical epilepsy evaluation. All scans were interpreted by one of the co-authors (H.C.). Four patients showed FMZ PET abnormality in only the temporal lobe (3 left, 1 right) in the absence of a MRI lesion (+PET/-MRI). Four patients showed only temporal lobe abnormalities (2 left, 2 right) on FMZ PET but also had an identifiable MRI lesion (+PET/+MRI). Data were retrospectively collected. The NP and PET exams occurred within 16 months of each other for all patients. The two groups were compared on demographic, medical, and measures of NP function. Descriptive, parametric, and nonparametric statistical analyses were utilized to assess group differences and relationship to temporal lobe FMZ PET abnormality.
There were no significant differences between the two groups for age of seizure onset, age at PET scan, and education. Nevertheless, age of seizure onset was substantially younger for the +PET/+MRI group (Mean = 8.0 vs. 20.5 years). There was also a significant difference in gender (p [lt] .05) with the +PET/-MRI and +PET/+MRI groups being comprised of 100% and 25% males, respectively. Group descriptive statistics showed the NP performance of the +PET/-MRI to be largely within normal limits save for mild impairment on a test of visuoconstruction and nonverbal memory. The +PET/+MRI however, showed impaired to borderline impaired scores on measures of verbal learning, confrontational naming, manual dexterity, visuoconstruction, and nonverbal memory. There was a clear but nonsignificant trend for the +PET/+MRI group to score lower (.5[ndash]18%) than the +PET/-MRI on most measures. Both groups performed relatively worse on measures of learning/memory and confrontational naming.
These preliminary data indicate greater cognitive impairment in patients who demonstrate functional temporal lobe abnormality in association with a structural lesion. The profile of cognitive difficulty was typical for dysfunction of the temporal lobes. There is a need to replicate this study with a larger series of patients and to compare the sensitivity among FMZ PET, MRI, and NP testing in corroborating epileptogenic focus.