Abstract
Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) may involve extrahippocampal areas of structural damage and dysfunction. The accuracy of medium-term spatial memory can be tested by memory-guided saccades (MGS) to evaluate a functional impairment of the parahippocampal cortex (PHC), while voxel-based morphometry (VBM) analysis can be used to detect a structural damage of the latter region. MGS with 3- and 30-s memorization delays were compared between 7 patients affected by right MTLE-HS (r-MTLE-HS), 6 patients affected by left MTLE-HS, and 13 healthy controls. The same subjects underwent brain MRI for a VBM analysis. Correlation analysis was performed between the results of VBM and MGS and with patients' clinical data. Right MTLE-HS patients showed impaired accuracy of leftward MGS with a 30-s memorization delay; their gray-matter volume was reduced in the right hippocampus and inferior temporal gyrus, and bilaterally in the cerebellum. Left MTLE-HS patients had normal MGS accuracy; their gray-matter volume was reduced in the left hippocampus, in the right-inferior temporal gyrus and corpus callosus, and bilaterally in the insular cortex and in the cerebellum. The difference between right and left parahippocampal volumes correlated with MGS accuracy, while right and left hippocampal volumes did not. Hippocampal and parahippocampal volume did not correlate with clinical variables such as febrile seizures, age at disease onset, disease duration, and seizure frequency. MGS abnormalities suggested the functional involvement of the right PHC in patients with r-MTLE-HS, supporting a right lateralization of spatial memory control and showing a relation between functional impairment and degree of atrophy.
Highlights
Extrahippocampal areas of structural damage may be detected in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), including the parahippocampal and mesial temporal lobe cortex [1,2,3,4,5].These findings have been emphasized in the MTLE-HS workshop promoted by the International League Against Epilepsy [6], when the importance of defining the site and characteristics of extrahippocampal damage was underlined
Our results showed in detail that the saccade velocity and latency values in MTLE-HS patients were not different from controls for all kind of saccades, suggesting that the cortical and brainstem mechanisms to program and trigger saccades were not affected
MTLE-HS patients do not differ from controls for the accuracy of reflexive saccades (RS) and of 3 memory-guided saccades (MGS): no differences could be found for the accuracy of the first saccade, and for the improvement that could be obtained after corrective saccades, and the capability to improve the accuracy of the first saccade (ED)
Summary
Extrahippocampal areas of structural damage may be detected in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), including the parahippocampal and mesial temporal lobe cortex [1,2,3,4,5]. These findings have been emphasized in the MTLE-HS workshop promoted by the International League Against Epilepsy [6], when the importance of defining the site and characteristics of extrahippocampal damage was underlined. Temporal lobe abnormalities were mainly ipsilateral to the epileptic focus, while extratemporal and subcortical abnormalities were bilateral This distribution of brain abnormalities in TLE patients is consistent with postmortem and fMRI imaging results. Hippocampal atrophy ipsilateral to the epileptic focus is the most common neuropathological correlate of TLE [8], and patients with right-sided epileptic focus are more likely to have bilateral hippocampal volume reduction [9]
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