The relationship between structural MRI, FDG-PET, and memory in temporal lobe epilepsy: Preliminary results

Multifocal hypometabolic correlates to deficits of verbal memory in mesial temporal lobe epilepsy

BACKGROUND AND OBJECTIVES

Neuropsychological research on mesial temporal lobe epilepsy (MTLE) often highlights material-specific memory deficits, but a lesion-focused model may not accurately reflect the underlying networks that support episodic memory in these patients. Our study evaluated the pathophysiology behind verbal learning/memory deficits as revealed by hypometabolism quantified through 18-fluorodeoxyglucose positron emission tomography (FDG-PET).

METHODS

This retrospective study included thirty presurgical patients with intractable unilateral MTLE who underwent interictal FDG-PET and verbal memory assessment (12 females, mean age: 38.73 years). Fluorodeoxyglucose-positron emission tomography mapping was performed with voxel-based mapping of glucose utilization to a database of age-matched controls to derive regional Z-scores. Neuropsychological outcome variables included scores on learning and recall trials of two distinct verbal memory measures validated for use in epilepsy research. Pearson's correlations evaluated relationships between clinical variables and verbal memory. Linear regression was used to relate regional hypometabolism and verbal memory assessment. Post hoc analyses assessed areas of FDG-PET hypometabolism (threshold Z ≤ -1.645 below mean) where verbal memory was impaired.

RESULTS

Verbal memory deficits correlated with hypometabolism in limbic structures ipsilateral to language dominance but also correlated with hypometabolism in networks involving the ipsilateral perisylvian cortex and contralateral limbic and nonlimbic structures.

DISCUSSION

We conclude that traditional models of verbal memory may not adequately capture cognitive deficits in a broader sample of patients with MTLE. This study has important implications for epilepsy surgery protocols that use neuropsychological data and FDG-PET to draw conclusions about surgical risks.

Functional Connectivity Alterations Based on Hypometabolic Region May Predict Clinical Prognosis of Temporal Lobe Epilepsy: A Simultaneous 18F-FDG PET/fMRI Study

(1) Background: Accurate localization of the epileptogenic zone and understanding the related functional connectivity (FC) alterations are critical for the prediction of clinical prognosis in patients with temporal lobe epilepsy (TLE). We aim to localize the hypometabolic region in TLE patients, compare the differences in FC alterations based on hypometabolic region and structural lesion, respectively, and explore their relationships with clinical prognosis. (2) Methods: Thirty-two TLE patients and 26 controls were recruited. Patients underwent 18F-FDG PET/MR scan, surgical treatment, and a 2−3-year follow-up. Visual assessment and voxel-wise analyses were performed to identify hypometabolic regions. ROI-based FC analyses were performed. Relationships between clinical prognosis and FC values were performed by using Pearson correlation analyses and receiver operating characteristic (ROC) analysis. (3) Results: Hypometabolic regions in TLE patients were found in the ipsilateral hippocampus, parahippocampal gyrus, and temporal lobe (p < 0.001). Functional alterations based on hypometabolic regions showed a more extensive whole-brain FC reduction. FC values of these regions negatively correlated with epilepsy duration (p < 0.05), and the ROC curve of them showed significant accuracy in predicting postsurgical outcome. (4) Conclusions: In TLE patients, FC related with hypometabolic region obtained by PET/fMRI may provide value in the prediction of disease progression and seizure-free outcome.

Temporal lobe dysfunction in late-onset epilepsy of unknown origin

OBJECTIVE

Epilepsy with onset in the adulthood is an increasing health problem, due to the progressive aging of the worldwide population. Whether the causes remain undetermined, the disease is defined as Late-Onset Epilepsy of Unknown origin (LOEU). The aim of this study was to evaluate the semiological, electroencephalographic, metabolic, and neuropsychological features of LOEU.

METHODS

We selected patients with late-onset epilepsy (LOE) (≥55 years), whose causes of the disease have been excluded with a deep clinical-instrumental characterization, including brain MRI, EEG, ¹⁸F-labeled fluoro-2-deoxyglucose positron emission tomography (FDG-PET), and neuropsychological assessment.

RESULTS

Twenty-three LOEU cases were retrospectively recruited. Half presented focal-onset seizures (FOS), the others focal to bilateral tonic-clonic seizures (FBTCS). All demonstrated a mild phenotype, with no recurrence of seizures on single antiseizure treatment at prolonged follow-up. Brain MRI scans were normal in 12 patients (52.3%) and showed nonspecific gliosis or mild atrophy in ten (43.5%); hippocampal sclerosis (HS) was observed in one. In 17/23 (73.9%), the EEG showed slow and/or epileptiform activity of the temporal areas. Brain FDG-PET revealed temporal lobe hypometabolism, mostly ipsilateral to EEG abnormal activity, or multifocal temporal and extra-temporal (cortical, subcortical and subtentorial) clusters of hypometabolism. The neuropsychological analysis demonstrated three different profiles: normal (43.5%), with focal deficits (39.1%) or mild multidomain impairment (17.4%).

SIGNIFICANCE

Late-Onset Epilepsy of Unknown origin can present as FOS or FBTCS, both with good prognosis. The application of metabolic imaging and neurophysiology techniques in these patients points to the dysfunction of the temporal structures, whose role in the pathogenetic process of the disease remains to be clarified.

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Functional brain network mechanism of executive control dysfunction in temporal lobe epilepsy

Background

Executive control dysfunction is observed in a sizable number of patients with temporal lobe epilepsy (TLE). Neural oscillations in the theta band are increasingly recognized as having a crucial role in executive control network. The purpose of this study was to investigate the alterations in the theta band in executive control network and explore the functional brain network mechanisms of executive control dysfunction in TLE patients.

Methods

A total of 20 TLE patients and 20 matched healthy controls (HCs) were recruited in the present study. All participants were trained to perform the executive control task by attention network test while the scalp electroencephalogram (EEG) data were recorded. The resting state signals were collected from the EEG in the subjects with quiet and closed eyes conditions. Functional connectivity among EEGs in the executive control network and resting state network were respectively calculated.

Results

We found the significant executive control impairment in the TLE group. Compared to the HCs, the TLE group showed significantly weaker functional connectivity among EEGs in the executive control network. Moreover, in the TLE group, we found that the functional connectivity was significantly positively correlated with accuracy and negatively correlated with EC_effect. In addition, the functional connectivity of the executive control network was significantly higher than that of the resting state network in the HCs. In the TLE group, however, there was no significant change in functional connectivity strengths between the executive control network and resting state network.

Conclusion

Our results indicate that the decreased functional connectivity in theta band may provide a potential mechanism for executive control deficits in TLE patients.