Effect of Seizure on Hippocampus in Mesial Temporal Lobe Epilepsy and Neocortical Epilepsy: MR Spectroscopy Study

Kim, Dong Wook; Lee, Sang Kun; Chung, Chun Kee; Song, In Chan; Chang, Kee Hyun

Abstract

PURPOSE
This study was performed to evaluate the effect of seizures on the bilateral hippocampus in mesial temporal lobe epilepsy (mTLE) and neocortical epilepsy by single voxel proton magnetic spectroscopy. METHODS: Forty-one patients with mTLE having unilateral hippocampal sclerosis and 43 patients with a neocortical epilepsy who underwent subsequent epilepsy surgery were recruited. Ninety-five percent confidence intervals of N-acetyl aspartate/choline (NAA/Cho) and NAA/creatine (NAA/Cr) ratios in 20 healthy control subjects were used as threshold values to determine abnormal NAA/Cho and NAA/Cr. The relationship between the results of MRS and the duration of epilepsy, the frequency of seizure, the effect of secondary generalized tonic clonic seizures (2GTCS), and the postsurgical outcome was evaluated. RESULTS: NAA/Cho and NAA/Cr were significantly lower in the ipsilateral hippocampus of mTLE and neocortical epilepsy. NAA/Cho was abnormally low in the ipsilateral hippocampus in 43.9% (18/41) and bilateral hippocampus in 26.8% of mTLE patients. Ipsilateral or bilateral abnormal NAA/Cr was detected in 46.3% (19/41) of mTLE. NAA/Cho was abnormally lower in the ipsilateral hippocampus in 27.9% and bilateral hippocampus in 41.9% of neocortical epilepsy patients. Ipsilateral or bilateral abnormal NAA/Cr was detected in 32.6% of the patients with neocortical epilepsy. Using AIs for patients with bilaterally abnormal ratios of NAA/Cho and NAA/Cr combined with unilateral abnormal ratio, the seizure focus was correctly lateralized in 65.9% of the patients with mTLE and 48.8% of neocortical epilepsy patients. Bilateral NAA/Cho abnormality was significantly related with a poor surgical outcome in mTLE. No significant relationship was found between the results of NAA/Cho or NAA/Cr and the surgical outcome in neocortical epilepsy. The mean contralateral NAA/Cr ratio of the hippocampus in mTLE was significantly lower in patients with a history of the secondary generalized tonic clonic seizure (2GTCS) than in those without it. CONCLUSIONS: Our results demonstrate functional abnormality of the hippocampus in neocortical epilepsy and the relation between 2GTCS and NAA/Cr of the contralateral hippocampus in mTLE. This proves the presence of the seizure effect on the hippocampus in neocortical epilepsy as well as in mTLE.