Temporal Lobe Epilepsy Phenotypes Associated With White Matter Covariance

Different cognitive phenotypes based on neuropsychological measures of language and memory are associated with distinct patterns of white matter abnormalities in patients with temporal lobe epilepsy, according to a study published in Neurology.

Investigators sought to characterize distinct cognitive phenotypes in patients with temporal lobe epilepsy based on patterns of language and memory impairment by evaluating alterations in white matter associated with each phenotype.

The study included 70 patients with temporal lobe epilepsy and 46 healthy controls with available neuropsychological data. Participants with epilepsy were characterized into 4 distinct cognitive phenotypes based on measures of language and memory: language and memory impaired (n=17), memory impaired only (n=14), language impaired only (n=20), and no impairment (n=19). Diffusion tensor imaging was obtained in all participants, and fractional anisotropy and mean diffusivity of both superficial and deep white matter tracts associated with memory and language were calculated for each phenotype. Both regional and network-based superficial white matter analyses were performed to determine whether cognitive phenotypes differed in their network microstructure.

Relative to healthy controls, distinct patterns of microstructural abnormalities in superficial white matter were found in the language and memory-impaired group and in the memory-impaired–only group. Only the language and memory-impaired group showed significant differences from the controls in fractional anisotropy and mean diffusivity in deep white matter tracts, along with altered superficial white matter networks. Participants with isolated language impairment demonstrated a relatively intact global superficial white matter network structure but had poor network structure within the classic language (perisylvian) regions. Participants with temporal lobe epilepsy and no impairment were similar to controls in all study measures.

Investigators point out limitations to the study are comprised of including only neuropsychological measures of language and memory and the fact that phenotypes were derived from neuropsychological criteria rather than using a data-driven approach.

The study findings show that distinct cognitive phenotypes were associated with unique patterns of white matter abnormalities (at both the regional and network levels) in patients with temporal lobe epilepsy. Investigators indicate future studies should perform a broader examination of different cognitive domains, as the ability to identify cognitive phenotypes can improve the treatment of epilepsy and its outcomes.

Reference

Reyes A, Kaestner E, Bahrami N, et al. Cognitive phenotypes in temporal lobe epilepsy are associated with distinct patterns of white matter network abnormalities [published online April 23, 2019]. Neurology. doi:10.1212/WNL.0000000000007370