The Regulation of Plasma Interleukin-6 Levels Is Modified by Hippocampal Sclerosis and Its Lateralization in Drug-Resistant Temporal Lobe Epilepsy

Abstract

Background. Several studies have reported the association of the proinflammatory cytokine IL-6 with temporal lobe epilepsy (TLE), but the regulation of IL-6 in hippocampal sclerosis (HS) is less studied. Objectives. To analyse IL-6 levels and the IL-6/IL-10 ratio in a larger, well-characterized group of patients with drug-resistant focal epilepsy (DRE), focusing especially on TLE and TLE-associated HS. Methods. IL-6 levels were measured by ELISA in plasma in a cross-sectional cohort of 265 patients comprising TLE with HS ( $n=34$ ), TLE without HS ( $n=103$ ), extratemporal lobe epilepsy ( $n=92$ ), and idiopathic generalized epilepsy ( $n=36$ ). Results. The IL-6/IL-10 ratio was higher in TLE with HS than in TLE without HS (3.1 vs. 1.6, $p=0.042$ ), whereas the median levels of IL-6 did not differ among epilepsy types. TLE without HS patients had a higher proportion of increased IL-6 levels than TLE with HS patients ( $p=0.021$ ). Additionally, IL-6 levels were higher in patients with right-sided HS than in those with left lateralization (1.71 vs. 0.80 pg/mL, $p=0.04$ ). In TLE with HS patients, IL-6 levels showed a negative correlation with seizure frequency during the last month ( $r=-0.342$ ; $p=0.047$ ), whereas in TLE without HS patients, the correlation was positive but did not reach significance ( $r=0.136$ ; $p=0.169$ ). Conclusion. IL-6 levels and the IL-6/IL-10 ratio are differentially regulated among patients with TLE depending on the presence of HS and its lateralization, suggesting that TLE with HS is a distinct category regarding cytokine activation.