Correlation of FDG PET Hypometabolism with Interictal Spike Frequency during FDG Distribution Phase in Temporal Lobe Epilepsy

ABSTRACT

BACKGROUND: Although hypometabolism of positron emission tomography (PET) helps lateralization of epileptic focus in temporal lobe epilepsy (TLE), the mechanism of PET hypometabolism (PET-Hypo) is still controversial. We investigated whether interictal spike frequency during distribution phase of 18F-fluorodeoxyglucose (DP-FDG) correlates with the degree of PET-Hypo in TLE. METHODS: FDG PET was performed in 21 TLE patients. In PET, polar, mesial, anterior, middle and posterior temporal ROIs (region of interests) were determined in superior, middle and inferior transtemporal planes. PET Asymmetry index (AI) of each ROI was obtained by (right-left)/(right+left) x 2. Scalp EEG was recorded from 30 min prior to FDG injection until the end of scanning. Interictal spikes on temporal electrodes (F7, F8, FT9, FT10, T3, T4, T5 and T6) were counted during DP-FDG. Left-Right difference of spike numbers on electrodes of both temporal regions was obtained by subtracting spike number of right temporal region from that of left side. RESULTS: Average number of interictal spikes during FDG-DP was 11.5 per patient. Distributions of spikes were anterior temporal (F7, F8, FT9, FT10)70.7%, mid-temporal (T3,T4)29.3%, posterior temporal (T5,T6)0%. Left-Right difference of spike number was strongly correlated with PET AI of whole temporal region (r=0.655, p=0.002). Lateralization of all PET-Hypo was concordant to that of interictal spike dominance during DP-FDG although 2 cases showed false lateralization of epileptic focus by PET. CONCLUSIONS: FDG PET hypometabolism was significantly correlated with DP-FDG interictal spike numbers. Anterior and polar temporal regions showed the best correlation. PET-Hypo may reflect not only permanent functional deficit but also transient regional cerebral dysfunction.