Diffusion tensor imaging correlates of memory and language impairments in temporal lobe epilepsy

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Abstract
Objective: To investigate the relationship between white matter tract integrity and language and memory performances in patients with temporal lobe epilepsy (TLE). Methods: Diffusion tensor imaging (DTI) was performed in 17 patients with TLE and 17 healthy controls. Fractional anisotropy (FA) and mean diffusivity (MD) were calculated for six fiber tracts (uncinate fasciculus [UF], arcuate fasciculus [AF], fornix [FORX], parahippocampal cingulum [PHC], inferior fronto-occipital fasciculus [IFOF], and corticospinal tract [CST]). Neuropsychological measures of memory and language were obtained and correlations were performed to evaluate the relationship between DTI and neuropsychological measures. Hierarchical regression was performed to determine unique contributions of each fiber tract to cognitive performances after controlling for age and hippocampal volume (HV). Results: Increases in MD of the left UF, PHC, and IFOF were associated with poorer verbal memory in TLE, as were bilateral increases in MD of the AF, and decreases in FA of the right AF. Increased MD of the AF and UF, and decreased FA of the AF, UF, and left IFOF were related to naming performances. No correlations were found between DTI measures and nonverbal memory or fluency in TLE. Regression analyses revealed that several fibers, including the AF, UF, and IFOF, independently predicted cognitive performances after controlling for HV. Conclusions: The results suggest that structural compromise to multiple fiber tracts is associated with memory and language impairments in patients with temporal lobe epilepsy. Furthermore, we provide initial evidence that diffusion tensor imaging tractography may provide clinically unique information for predicting neuropsychological status in patients with epilepsy. GLOSSARY: AF = arcuate fasciculus; BNT = Boston Naming Test; CST = corticospinal tract; DTI = diffusion tensor imaging; FA = fractional anisotropy; FORX = fornix; HV = hippocampal volume; ICHV = intracranial-adjusted HV; IFOF = inferior fronto-occipital fasciculus; LM = Logical Memory; MD = mean diffusivity; MTS = mesial temporal sclerosis; PHC = parahippocampal cingulum; TLE = temporal lobe epilepsy; UF = uncinate fasciculus; WMS-III = Wechsler Memory Scale–Third Edition.