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Abstract
Objective: To define the functional network changes that characterize MRI-negative temporal lobe epilepsy (TLE) and TLE with hippocampal sclerosis (HS-TLE).
Methods: We studied 36 patients with medically refractory unilateral TLE, having either a normal clinical MRI (n = 18) or unilateral hippocampal sclerosis (n = 18). Patients were compared to healthy controls of equivalent age and sex (n = 27). Functional connectivity in 10 minutes of task-free functional MRI was assessed using a voxel-resolution graph theoretic analysis, using the metrics of degree, clustering coefficient, eigenvector, and betweenness centrality. Significant clusters were further explored with a seed-based analysis.
Results: MRI-negative TLE showed decreased connectivity at the ipsilateral superior and middle temporal gyri compared to controls (decreased eigenvector centrality). No functional abnormality was detected within mesial temporal structures. In contrast, HS-TLE showed increased connectivity within the affected hippocampus and anterior thalamus (increased clustering coefficient) and decreased connectivity of the ventromesial prefrontal cortex (decreased betweenness centrality). Using the detected clusters as seed regions revealed decreased connectivity from the sclerotic hippocampus to both the contralateral temporal lobe and regions of the default mode network.
Conclusion: MRI-negative TLE is associated with impaired interictal connectivity of the temporal neocortex, lateralized to the epileptic side. HS-TLE shows a different pattern, with functional segregation of the sclerotic hippocampus and impairment of its long-range connectivity. This suggests that MRI-negative TLE is not merely a subtle version of hippocampal sclerosis, but is rather a separate condition that involves distinct brain networks.
GLOSSARY
- fMRI=
- functional MRI;
- FWE=
- family-wise error;
- FWHM=
- full width at half maximum;
- HS=
- hippocampal sclerosis;
- ROI=
- region of interest;
- TE=
- echo time;
- TLE=
- temporal lobe epilepsy;
- TR=
- repetition time;
- vmPFC=
- ventromesial prefrontal cortex
Footnotes
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Supplemental data at Neurology.org
- Received March 23, 2016.
- Accepted in final form July 14, 2016.
- © 2016 American Academy of Neurology
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