Proton magnetic resonance spectroscopy in MRI-negative temporal lobe epilepsy.

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 approximately 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/(choline-creatine + 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.