Abstracts

Rationale: Preictal neurovascular changes have been noted in patients with epilepsy including increases in cerebral perfusion¹ and blood flow² in the epileptic lobe occurring from seconds to minutes prior to seizure onset. Our group has demonstrated vascular changes measured in the 15 min prior to seizure onset from the frontal lobe ipsilateral to the presumed seizure focus. This was done in patients with temporal lobe epilepsy (TLE) using near infrared spectroscopy (NIRS)³. These studies have examined few participants. We aimed to characterize preictal vascular changes occurring in the frontal lobes of a larger group of patients with TLE using NIRS.Methods: Eight participants (3F/5M age: 39.5 13.9 years) were recruited from the Calgary Epilepsy Program, from whom 10 temporal lobe seizures were recorded. Two optodes were placed on the forehead of all but 1 participant, where 1 optode was placed on the forehead ipsilateral to the presumed seizure focus. A NIRO-200 oximeter was used to obtain continuous measures of the relative concentrations of oxyhemoglobin (HbO₂), deoxyhemoglobin (HHb), oxygen saturation, and total hemoglobin (HbT) until a seizure occurred. Data were low pass filtered with a cutoff of 0.5 Hz and averaged across 1 min bins for the 30 min prior to seizure onset. Data were normalized by subtracting the mean over the 30 min prior to seizure onset. The Wilcoxon Signed-Rank Test was implemented using SPSS to compare each preictal minute to baseline, defined as the minute prior to seizure onset. No corrections were made for multiple comparisons. Similarity in preictal changes between pairs of data was assessed using Spearman s rank correlation coefficient.Results: HbO₂ values were decreased in the minute prior to seizure onset compared to 27 min prior to seizure onset in the frontal lobe ipsilateral to seizure onset (p=0.038). Contralateral HbO₂ was decreased in the minute prior to seizure onset compared to preictal min 2 (p=0.017), 15 (p=0.036), and 18 (p=0.017). HHb was also decreased in the minute prior to seizure onset compared to preictal minute 2 (p=0.012). Two seizures occurred during the same day for Participant 4. Ipsilateral HbO₂, HHb, and HbT from both seizures were correlated (p<0.001) along with contralateral HbT (p<0.01).Conclusions: Measurable vascular changes occur prior to seizure onset, however, the results are variable. It is possible that patient heterogeneity is obscuring trends within the data. The reproducibility of vascular changes in the single patient in whom 2 seizures were captured on the same day are encouraging. Although these data are difficult to acquire, future work should include the examination of preictal vascular changes from multiple seizures in the same person as well as more participants to allow for subdivisions into more homogenous groups. Funding: CIHR, Savoy Foundation References: 1. Baumgartner et al. J Nucl Med 1998; 39(6):978-82. 2. Weinand et al. J Neurosurg 1997; 86(2):226-32. 3. Slone et al. Epileptic Disord 2012; 14(4):371-8.