Uncoupling of blood flow and metabolism in focal epilepsy

Purpose: Interictal measurements of cerebral blood flow are less helpful in localizing epileptic foci than are measurements of brain metabolism. This may be related to an uncoupling of blood flow and metabolism. In this study , brain metabolism and blood flow were compared in an acute experimental mo del of focal interictal epilepsy. Methods: Interictal epileptic foci were induced by an epicortical applicati on of penicillin in rats. After 1 h, stereotyped interictal activity was in itiated, lasting until the end of the experiment. Brain metabolism was dete rmined with [C-14]deoxyglucose, and cerebral blood flow with [C-14]iodoanti pyrine autoradiography. Results: In control experiments, metabolism and blood flow were coupled. In animals with focal interictal epileptic activity, the metabolism was stron gly increased in the focus and reduced in areas lateral to the focus. In co ntralateral brain areas, blood flow and metabolism varied in a parallel fas hion. Ipsilateral to the focus, however, blood flow and metabolism were alt ered disproportionately. In the focus, the increase of blood flow was less marked than the increase of metabolism, and the area with increased blood f low was larger than the area with increased metabolism. Lateral to the focu s, in the area with a hypometabolism, blood flow was not concomitantly redu ced. Conclusions: The experiments show that blood flow and metabolism in focal e pilepsy may be uncoupled in widespread regions. This is due neither to stru ctural abnormalities nor to the duration or discharge pattern of epileptic activity. The results explain why interictal metabolic investigations have a higher predictive value in presurgical epilepsy evaluation than do interi ctal measurements of blood flow.