Magnetoencephalographic and Magnetic Resonance Spectroscopy Evidence of Regional Functional Abnormality in Mesial Temporal Lobe Epilepsy

Abstract

Mesial temporal lobe epilepsy (mTLE) with mesial temporal sclerosis (MTS) is a recognized epilepsy syndrome which is successfully treated with mesial temporal lobe resection. However, recent studies suggest that mTLE is more than a "focal" disease process. The objective of our study was to determine the presence and extent of functional abnormalities outside of a defined structural abnormality in epilepsy patients with mTLE. We used a prospective age-matched controlled design to study eight consecutive patients with MTS who were undergoing epilepsy surgery evaluation. Magnetoencephalography was used to localize the sources of electromagnetic abnormality. Proton magnetic resonance spectroscopy ((1)H-MRS) measured integrated peak areas for N-acetyl compounds (NAA) and choline-containing compounds (Cho) to determine regions of metabolic abnormality. All eight subjects had predominant electromagnetic abnormality in the temporal lobe ipsilateral to the MTS. All eight subjects had lower NAA/Cho ratios in the region of electromagnetic abnormality when compared to the homologous contralateral region (P < 0.001). Four subjects had predominant MEG spiking outside the mesial temporal region. Surgery-free outcome for the group with neuroimaging abnormalities outside of the medial temporal lobe is 50%. The region of maximal electromagnetic abnormality is outside the hippocampus in some patients with mTLE. These regions also demonstrate functional abnormalities. Our findings support the concept that mTLE is a more diffuse process than the hippocampal structural abnormality, which may impact surgical outcome.

Proton magnetic resonance spectroscopy in patients with solitary and sporadic temporal lobe epileptic seizures

“…Our results were based on data collected from a small set of 10 patients. Based on our experience we believe that 1 H MRS could be a useful paraclinic method not only in patients with refractory epilepsy, but also in patients suffering from solitary or sporadic epileptic seizures generated in the temporal lobe (Chernov et al 2009;Shih et al 2011).…”

“…One of the most common diagnoses where the 1 H MRS is applied is epilepsy (Starčuk et al 2005;Fojtíková et al 2007;Shih et al 2011).…”

Temporal pole proton preoperative magnetic resonance spectroscopy in patients undergoing surgery for mesial temporal sclerosis

“…However, the histological examination of the temporal lobe white matter in their series showed no abnormalities. 17 Similarly, Shih et al 23 reported their results from a series of 8 patients with MTS who underwent proton MRS of the lateral temporal lobe. These authors found that the NAA concentration was lower in the lateral temporal lobe on the same side as the MTS in 50% of their cases, while the concentration of Cho was increased in these patients.…”

“…Several clinical investigators have demonstrated with the aid of proton MRS that in cases of MTS, the ipsilateral extrahippocampal temporal lobe may have altered metabolism. 6,[17][18][19]23,24,26 Meiners et al 17 reported their experience with a series of 11 patients with hippocampal sclerosis who underwent single-voxel extrahippocampal temporal lobe proton MRS (Table 3). They found that the white matter of the temporal lobe ipsilateral to the hippocampal sclerosis demonstrated decreased concentrations of NAA, marked increase in Cho concentrations, a slight increase in Cr concentrations, and decreased NAA/Cho and NAA/Cr ratios.…”

“…3,6,15,[17][18][19]23,24,26 Proton MRS is a noninvasive diagnostic tool that may provide valuable information regarding the biochemical profile and the metabolism of the brain. It has been extensively used in the preoperative evaluation of patients with medically intractable epilepsy, especially in cases of TLE, with varying specificity and accuracy rates.…”