Interictal regional slow activity in temporal lobe epilepsy correlates with lateral temporal hypometabolism as imaged with 18FDG PET: neurophysiological and metabolic implications

摘要

OBJECTIVES—Thephenomenon of interictal regional slow activity (IRSA) in temporal lobeepilepsy and its relation with cerebral glucose metabolism, clinicaldata, MRI, and histopathological findings was studied.
METHODS—Interictal18F-fluorodeoxyglucose positron emission tomography(FDG PET) was performed under continuous scalp EEG monitoring in 28 patients with temporal lobe epilepsy not associated with intracranialforeign tissue lesions, all of whom subsequently underwent resectivesurgery. Regions of interest (ROIs) were drawn according to a standardtemplate. IRSA was considered lateralised when showing a 4:1 or greaterratio of predominance on one side.
RESULTS—Sixteenpatients (57%) had lateralised IRSA which was always ipsilateral tothe resection and of maximal amplitude over the temporal areas. Itspresence was significantly related to the presence of hypometabolism inthe lateral temporal neocortex (p=0.0009). Logistic regression of theasymmetry indices for all measured cerebral regions confirmed a strongassociation between IRSA and decreased metabolism of the posteriorlateral temporal neocortex only (p=0.009). No significant relationcould be shown between slow activity and age at onset, duration of theepilepsy, seizure frequency, and MRI evidence for hippocampal atrophy.Furthermore, IRSA was not specifically related to mesial temporalsclerosis or any other pathology.
CONCLUSIONS—Interictalregional slowing in patients with temporal lobe epilepsy not associatedwith a mass lesion is topographically related to the epileptogenic areaand therefore has a reliable lateralising, and possibly localising,value. Its presence is irrelevant to the severity or chronicity of theepilepsy as well as to lateral deactivation secondary to neuronal lossin the mesial temporal structures. Although slow EEG activity isgenerally considered as a non-specific sign of functional disturbance,interictal regional slowing in temporal lobe epilepsy should beconceptualised as a distinct electrographic phenomenon which isdirectly related to the epileptogenic abnormality. The strongcorrelation between interictal regional slowing and lateral temporalhypometabolism suggests in turn that the second may delineate a fieldof reduced neuronal inhibition which can receive interictal and ictal propagation.