Extrahippocampal gray matter loss and hippocampal deafferentation in patients with temporal lobe epilepsy.
OBJECTIVE
Medial temporal epilepsy (MTLE) is associated with extrahippocampal brain atrophy. The mechanisms underlying brain damage in MTLE are unknown. Seizures may lead to neuronal damage, but another possible explanation is deafferentation from loss of hippocampal connections. This study aimed to investigate the relationship between hippocampal deafferentation and brain atrophy in MTLE.


METHODS
Three different MRI studies were performed involving 23 patients with unilateral MTLE (8 left and 15 right) and 34 healthy controls: (1) voxel-based morphometry (VBM), (2) diffusion tensor imaging (DTI) and (3) probabilistic tractography (PT). VBM was employed to define differences in regional gray matter volume (GMV) between controls and patients. Voxel-wise analyses of DTI evaluated differences in fractional anisotropy (FA), mean diffusivity (MD) and hippocampal PT. Z-scores were computed for regions-of-interest (ROI) GMV and peri-hippocampal FA and MD (to quantify hippocampal fiber integrity). The relationship between hippocampal deafferentation and regional GMV was investigated through the association between ROI Z scores and hippocampal fiber integrity.


RESULTS
Patients with MTLE exhibited a significant reduction in GMV and FA in perihippocampal and limbic areas. There was a decrease in hippocampal PT in patients with MTLE in limbic areas. A significant relationship between loss of hippocampal connections and regional GMV atrophy was found involving the putamen, pallidum, middle and inferior temporal areas, amygdala and ceberellar hemisphere.


CONCLUSIONS
There is a relationship between hippocampal disconnection and regional brain atrophy in MTLE. These results indicate that hippocampal deafferentation plays a contributory role in extrahippocampal brain damage in MTLE.
Bonilha
Leonardo
L
Division of Neurology, Department of Neurosciences, Medical University of South Carolina, Charleston, SC 29425, USA. bonilha@musc.edu
Edwards
Jonathan C
JC
Kinsman
Stephen L
SL
Morgan
Paul S
PS
Fridriksson
Julius
J
Rorden
Chris
C
Rumboldt
Zoran
Z
Roberts
Donna R
DR
Eckert
Mark A
MA
Halford
Jonathan J
JJ
D000328:Adult; D000344:Afferent Pathways / Q000473:pathology*; D000679:Amygdala / Q000473:pathology; D001284:Atrophy; D001931:Brain Mapping / Q000379:methods; D002531:Cerebellum / Q000473:pathology; D002540:Cerebral Cortex / Q000473:pathology; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D004292:Dominance, Cerebral / Q000502:physiology; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000473:pathology*; D005260:Female; D006179:Gyrus Cinguli / Q000473:pathology; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008032:Limbic System / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology; D020534:Parahippocampal Gyrus / Q000473:pathology; D011699:Putamen / Q000473:pathology; D012598:Sclerosis; D013702:Temporal Lobe / Q000473:pathology*; D013788:Thalamus / Q000473:pathology