Hyperphosphorylated Tau in Mesial Temporal Lobe Epilepsy: a Neuropathological and Cognitive Study

Temporal lobe epilepsy (TLE) often courses with cognitive deficits, but its underlying neuronal basis remains unclear. Confluent data suggest that epilepsy share pathophysiological mechanisms with neurodegenerative diseases. However, as most studies analyze subjects 60 years old and older, it is challenging to rule out that neurodegenerative changes arise from age-related mechanisms rather than epilepsy in these individuals. To fill this gap, we conducted a neuropathological investigation of the hippocampal formation of 22 adults with mesial TLE and 20 age- and sex-matched controls (both younger than 60 years). Moreover, we interrogated the relationship between these neuropathological metrics and cognitive performance. Hippocampal formation extracted from patients with drug-resistant mesial TLE undergoing surgery and postmortem non-sclerotic hippocampal formation of clinically and neuropathologically controls underwent immunohistochemistry against amyloid β (Aβ), hyperphosphorylated tau (p-tau), and TAR DNA-binding protein-43 (TDP-43) proteins, followed by quantitative analysis. Patients underwent a comprehensive neuropsychological evaluation prior to surgery. TLE hippocampi showed a significantly higher burden of p-tau than controls, whereas Aβ deposits and abnormal inclusions of TDP-43 were absent in both groups. Patients with hippocampal sclerosis (HS) type 2 had higher immunostaining for p-tau than patients with HS type 1. In addition, p-tau burden was associated with impairment in attention tasks and seizures frequency. In this series of adults younger than 60 years-old, the increase of p-tau burden associated with higher frequency of seizures and attention impairment suggests the involvement of tau pathology as a potential contributor to cognitive deficits in mesial TLE.