Relationship between hypometabolic patterns and ictal scalp EEG patterns in patients with unilateral hippocampal sclerosis: An FDG-PET study

This study was to explore the relationship between scalp ictal EEG patterns and interictal hypometabolic patterns in hippocampal sclerosis-associated mesial temporal lobe epilepsy (HS-MTLE) and determine the clinical significance of interictal hypometabolic patterns. Twenty-five patients were classified into 2 groups based on initial ictal discharge (IID) frequency on scalp EEG: (a) those with a sustained regular 5- to 9-Hz rhythm with a restricted temporal or subtemporal distribution (group 1, N = 9); and (b) those with an irregular 2- to 5-Hz rhythm with a widespread distribution (group 2, N = 16). Using statistical parametric mapping, the PET results of each group were compared with age- and sex-matched controls to identify regions of significant hypometabolism, and the clinical characteristics were compared. Group 1 showed focal hypometabolism confined to the ipsilateral temporal lobe, whereas group 2 showed widespread hypometabolism in the ipsilateral temporal lobe, insular cortex and anterior part of the putamen. The two groups showed no significant differences in clinical characteristics. Among semiologic features, dystonic limb posturing was more frequently observed in group 2 (p = 0.03). In summary, scalp EEG IID patterns in HS-MTLE can be important in determining hypometabolic patterns on interictal PET. Differences in hypometabolic patterns may reflect preferential pathways of ictal propagation rather than intrinsic epileptogenic regions.