Purpose: In refractory temporal lobe epilepsy (rTLE), gray matter (GM) abnormalities are not confined to the hippocampus but also are found in extrahippocampal structures. Very recently we observed in mild TLE (mTLE) with or without mesiotemporal sclerosis (MTS), GM reductions in regions outside the presumed epileptogenic focus. To date, there are no studies that directly investigate whether whole-brain GM volume differs between rTLE and mTLE. Herein, we used optimized voxel-based morphometry (VBM) to identify GM abnormalities beyond the hippocampus in both rTLE and mTLE with evidence of MTS.
Methods: Brain magnetic resonance imaging (MRI) and optimized VBM were performed in 19 unrelated patients with mTLE, 19 patients with rTLE, and 37 healthy controls. MRI diagnosis of MTS was based on the atrophy of the hippocampal formation and/or mesiotemporal hyperintensity on fluid-attenuated inversion recovery (FLAIR) or T(2) images, or both.
Results: No patients (rTLE and mTLE) had generalized tonic-clonic or complex partial seizures for at least 3 weeks before scanning. Both mTLE and rTLE patients showed GM volume reduction of the bilateral thalamus, left hippocampus, and sensorimotor cortex compared with controls. No significant GM difference was found between rTLE and mTLE groups.
Discussion: In both rTLE and mTLE, VBM shows GM reductions not confined to the hippocampus involving mainly the thalamus bilaterally. This finding together with the lack of significant GM differences between the two TLE groups supports the hypothesis that mTLE and rTLE might lie along a biologic continuum, suggesting a pathophysiologic role of the thalamus in partial epilepsy.