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.