Short echo time single-voxel H-1 magnetic resonance spectroscopy in magnetic resonance imaging negative temporal lobe epilepsy: Different biochemicalprofile compared with hippocampal sclerosis

Single-voxel proton magnetic resonance spectroscopy (H-1 MRS) has shown abn ormalities in patients with temporal lobe epilepsy (TLE) and hippocampal sc lerosis (HS). Many TLE patients, however, do not have HS or other lesions o n quantitative magnetic resonance imaging (MRI) (MRI-negative). Fifteen con trol subjects, 15 patients with unilateral HS, and 15 MRI-negative TLE pati ents underwent H-1 MRS at an echo time of 30 msec on a 1.5-T GE Sigma scann er. Voxels were tailored to the individual hippocampi. N-Acetylaspartate (N AA), creatine, choline, total glutamate plus glutamine (Glx), and myo-inosi tol (Ins) were quantitated by using an external standard and LCModel, a use r-independent quantitation method. Normal ranges were defined as the contro l mean +/- 2.5 SD. In HS patients, 12 of 15 had abnormally low NAA in scler otic hippocampi; 3 of these 12 also had abnormally low NAA contralaterally. Abnormally low NAA/Ins ratios lateralized the side affected by HS in 7 of 15 patients, without any bilateral abnormalities. In 15 MRI-negative TLE pa tients, 4 had abnormally low hippocampal NAA ipsilateral to seizure onset, 1 of whom had abnormally low NAA bilaterally. Analysis of groups of subject s showed a bilateral decrease in NAA, most marked in patients with HS and o n the side of seizure onset. The mean NAA/Ins ratio was lower in patients w ith HS than in control subjects and in MRI-negative patients. The concentra tion of Glx was higher ipsilateral to seizure onset in MRI-negative patient s than in HS patients. Quantitative short echo time H-1 MRS identified abno rmalities in 87% of patients with HS and 27% of MRT-negative TLE patients i n concordance with other lateralizing data. In individual and group compari sons, H-1 MRS described a metabolite profile in the hippocampi of MRI-negat ive TLE patients that was different from patients with HS, with an increase in Glx and a less marked decrease in NAA than was seen in HS.