Proton magnetic resonance spectroscopy in MRI-negative temporal lobe epilepsy

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Abstract
Objective: To determine the 1H MRS findings in patients with intractable temporal lobe epilepsy (TLE) who had no detectable abnormality on either qualitative or quantitative MRI. Background: Previous work has indicated that ∼20% of patients with TLE remain MRI negative after extensive qualitative and quantitative investigation. Single-voxel 1H MRS provides a means of identifying potentially diffuse disease. Methods: Seven patients with intractable TLE, normal routine MRI, normal hippocampal volumes, and normal hippocampal and amygdala quantitative T2 values underwent single-voxel 1H MRS of the medial temporal lobes. The results are compared with those from 13 control subjects and 15 patients with evidence of hippocampal sclerosis (HS). Results: The ratio N-acetylaspartate/(cholinecreatine + phosphocreatine) was abnormally low in five of the seven MRI-negative patients. In two of these patients, the ratios were low bilaterally. The observed MRS ratios in the MRI-negative group with abnormal EEG were similar to those from temporal lobes ipsilateral to HS, suggesting the presence of widespread or diffuse disease of a similar degree in both groups. Conclusions: These results demonstrate that MRS can provide evidence of temporal lobe abnormalities in TLE patients who show no abnormality on extensive MRI investigation.