ELSEVIER Magnetic Resonance Imaging, Vol. 15, No. 4, pp. 475-478, 1997 Copyright 0 1997 Elsevier Science Inc. Printed in the USA. All rights reserved 0730-725x/97 $17.00 + .oo PI1 SO730-725X( 96) 00327-8 l Original Contribution CORRELATION OF SEIZURE FREQUENCY WITH N-ACETYL- ASPARTATE ‘LEVELS DETERMINED BY ‘H MAGNETIC RESONANCE SPECTROSCOPIC IMAGING P.A. GARCIA,* K.D. LAXER,* J. VAN DER GROND,~ J.W. HUGG,~ G.B. MATSONS AND M.W. WEINER/~ *Department of Neurology, University of California, San Francisco, California, USA, TDepartment of Radiology, Academic Hospital Utrecht, $Department of Neurology, University of Alabama, Birmingham, Alabama, USA, Department of Pharmaceutical Chemistry, University of California, San Francisco, California, USA, Department of Medicine, University of California, San Francisco, California, USA Using ‘H MRSI, we measured N-acetyl-aspartate (NAA), a neuronal marker, in the seizure focus of 16 patients with partial epilepsy. Decreasing NAA correlated with increasing seizure frequency in frontal lobe epilepsy (t = -0.72, p < 0.02) and a similar trend was present in temporal lobe epilepsy (r = -.60, p < 0.06). NAA was not related to the duration of epilepsy. We conclude that patients with higher seizure frequency have evidence of greater neuron loss or dysfunction. 0 1997 Elsevier Science Inc. Keywords: MRSI, magnetic resonance spectroscopic imaging; Seizure frequency; Epilepsy; Spectroscopy. INTRODUCTION Many patients with partial epilepsy experience recur- rent seizures despite treatment with anticonvulsants. In these patients, seizure frequency and duration of epilepsy are measures of clinical severity. Seizure fre- quency correlates with the probability of seizure remis- sion’ as well as the perception of well-being.’ Unfortu- nately, we do not understand how the clinical severity is related to the pathological substrate. Proton magnetic resonance spectroscopic imaging (‘H MRSI) permits non-invasive measurement of N- acetyl-aspartate (NAA), a neuronal marker. ‘H MRSI consistently demonstrates decreased NAA in condi- tions characterized by neuronal loss such as partial epilepsy,3 stroke4 and glial tumors.5 In animal models of status epilepticus, NAA measurements correlate with pathologically determined neuron 10~s.~ We de- signed this study to determine whether NAA is related to seizure frequency or epilepsy duration in patients with partial epilepsy. METHODS Sixteen patients with medically refractory partial epilepsy [eight with frontal lobe epilepsy (FLE) and eight with temporal lobe epilepsy (TLE)] consented to be studied (Table 1) . Patients with expanding mass lesions on MRI were excluded. One patient with FLE had a cavernous angioma. Two TLE patients showing hippocampal T2 signal prolongation without mass ef- fect had small gangliogliomas discovered on patholog- ical examination. Seizure localization was determined by ictal electroencephalographic (EEG) recordings which were sufficiently localizing for the patient to be considered a candidate for surgical resection. All but two of the patients with FLE required intracranial re- cordings to fulfill the criteria while the TLE patients had adequate localization with scalp EEG recordings. NAA in all of these patients had previously been found to be decreased in the epileptogenic focus compared to the contralateral homologous region.3,7 MRI and MRSI studies were performed using a Gyroscan S15 whole body imaging and spectroscopy RECEIVED 311196: ACCEPTED 91496. Avenue, University of California, San Francisco, Box 0138, Address correspondence to Paul A. Garcia, MD, Northern San Francisco, CA 94143-0138, email address: garfish@ California Comprehensive Epilepsy Center, 400 Parnassus itsa.ucsf.edu 415