The predictive value of hypometabolism in focal epilepsy: a prospective study in surgical candidates
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FDG PET is an established tool in presurgical epilepsy evaluation, but it is most often used selectively in patients with discordant MRI and EEG results. Interpretation is complicated by the presence of remote or multiple areas of hypometabolism, which leads to doubt as to the true location of the seizure onset zone (SOZ) and might have implications for predicting the surgical outcome. In the current study, we determined the sensitivity and specificity of PET localization prospectively in a consecutive unselected cohort of patients with focal epilepsy undergoing in-depth presurgical evaluation.
A total of 130 patients who underwent PET imaging between 2006 and 2015 matched our inclusion criteria, and of these, 86 were operated on (72% with a favourable surgical outcome, Engel class I). Areas of focal hypometabolism were identified using statistical parametric mapping and concordance with MRI, EEG and intracranial EEG was evaluated. In the surgically treated patients, postsurgical outcome was used as the gold standard for correctness of localization (minimum follow-up 12 months).
PET sensitivity and specificity were both 95% in 86 patients with temporal lobe epilepsy (TLE) and 80% and 95%, respectively, in 44 patients with extratemporal epilepsy (ETLE). Significant extratemporal hypometabolism was observed in 17 TLE patients (20%). Temporal hypometabolism was observed in eight ETLE patients (18%). Among the 86 surgically treated patients, 26 (30%) had hypometabolism extending beyond the SOZ. The presence of unilobar hypometabolism, included in the resection, was predictive of complete seizure control (p = 0.007), with an odds ratio of 5.4.
Additional hypometabolic areas were found in one of five of this group of nonselected patients with focal epilepsy, including patients with “simple” lesional epilepsy, and this finding should prompt further in-depth evaluation of the correlation between EEG findings, semiology and PET. Hypometabolism confined to the epileptogenic zone as defined by EEG and MRI is associated with a favourable postoperative outcome in both TLE and ETLE patients.
KeywordsFDG PET Temporal epilepsy Extratemporal epilepsy Prognosis Predictive value Seizure onset zone
Positron emission tomography
Magnetic resonance imaging
Temporal lobe epilepsy
Extratemporal lobe epilepsy
Seizure onset zone
Statistical parametric mapping
J.T. was supported by the “Egas Moniz” grant of the Neurology Portuguese Society. M.S. was supported by SNF 113766, SNF 180365, SNF 163398. Statistical help was provided by the Clinical Research Center, Geneva University Hospitals (Prof. Thomas Perneger). The reference database was provided by the CERMEP-Imagerie du vivant, Lyon, France.
J.T., M.S. and V.G. contributed to the concept and study design. M.S. and F.Picard. were responsible for patient management. J.T., F.Pittau, F.Picard, M.I.V., M.S. and V.G. contributed to data acquisition and analysis. J.T. and V.G. drafted the manuscript, tables and figures. F.Pittau, A.H., S.B., F.Picard, M.I.V., F.S. and M.S. contributed to critical revision of the manuscript. All authors approved the final version.
Compliance with ethical standards
This study was approved by the Geneva Cantonal Ethics Commission, and was in accordance with the principles of the Declaration of Helsinki and its further amendments.
Conflicts of interests
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