Earlier seizure onset and longer epilepsy duration correlate with the degree of temporal hypometabolism in patients with mesial temporal lobe sclerosis.

OBJECTIVE: To study the relationship of glucose metabolism and volume of the temporal lobes with age at epilepsy onset, epilepsy duration, and seizure frequency in patients with mesial temporal sclerosis (MTS).

METHODS: We evaluated the pre-surgical 18 F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) and magnetic resonance imaging (MRI) of 18 patients with epilepsy and MRI findings of MTS, who were seizure-free for at least 2-years after temporal lobectomy. We calculated the volume of the hippocampi and amygdalae on MRI. On PET we studied their mean standard uptake values (SUV), and relative metabolic activity as compared to normal subjects in terms of Z-scores. We compared the PET and MRI metrics in the bilateral structures using the Wilcoxon sign rank test. We studied the relationship between the imaging metrics and age of epilepsy onset, epilepsy duration, and seizure frequency via Spearman correlation analyses.

RESULTS: Younger age at onset correlated with decreased hippocampal glucose metabolism (rs=0.64, p=0.008). Longer epilepsy duration correlated with decreased hippocampal glucose metabolism (rs=-0.55, p=0.024). There was no correlation between age at onset of epilepsy, epilepsy duration, or seizure frequency and volumetrics. Z-score in the sclerotic hippocampus (-3.51±2.2vs -0.7±1.7) and amygdala (-3.26±2.3 vs -0.68±1.8) was smaller than the contralateral (p<0.001). The diseased hippocampus (2.84±0.49 vs 3.52±0.4ml) and ipsilateral amygdala (1.49±0.24 vs 1.72±0.3ml) were significantly smaller than the contralateral (p<0.02).

SIGNIFICANCE: Earlier epilepsy onset correlated with hippocampal hypometabolism. Longer epilepsy duration correlated with amygdalar hypometabolism suggesting an ongoing progressive disease in MTLE.