Modur Pradeep N
Department of Neurology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Ann Indian Acad Neurol. 2014 Mar;17(Suppl 1):S99-S106. doi: 10.4103/0972-2327.128674.
In pre-surgical evaluation of epilepsy, there has been an increased interest in the study of electroencephalogram (EEG) activity outside the 1-70 Hz band of conventional frequency activity (CFA). Research over the last couple of decades has shown that EEG activity in the 70-600 Hz range, termed high frequency oscillations (HFOs), can be recorded intracranially from all brain regions both interictally and at seizure onset. In patients with epilepsy, HFOs are now considered as pathologic regardless of their frequency band although it may be difficult to distinguish them from the physiologic HFOs, which occur in a similar frequency range. Interictal HFOs are likely to be confined mostly to the seizure onset zone, thus providing a new measure for localizing it. More importantly, several studies have linked HFOs to underlying epileptogenicity, suggesting that HFOs can serve as potential biomarkers for the illness. Along with HFOs, analysis of ictal baseline shifts (IBS; or direct current shifts) and infraslow activity (ISA) (ISA: <0.1 Hz) has also attracted attention. Studies have shown that: IBSs can be recorded using the routine AC amplifiers with long time constants; IBSs occur at the time of conventional EEG onset, but in a restricted spatial distribution compared with conventional frequencies; and inclusion of IBS contacts in the resection can be associated with favorable seizure outcome. Only a handful of studies have evaluated all the EEG frequencies together in the same patient group. The latter studies suggest that the seizure onset is best localized by the ictal HFOs, the IBSs tend to provide a broader localization and the conventional frequencies could be non-localizing. However, small number of patients included in these studies precludes definitive conclusions regarding post-operative seizure outcome based on selective or combined resection of HFO, IBS and CFA contacts. Large, preferably prospective, studies are needed to further evaluate the implications of different EEG frequencies in epilepsy.
在癫痫的术前评估中，人们对传统频率活动（CFA）1-70Hz频段以外的脑电图（EEG）活动研究兴趣日增。过去几十年的研究表明，70-600Hz范围内的EEG活动，即高频振荡（HFOs），可在发作间期和发作开始时从颅内所有脑区记录到。在癫痫患者中，HFOs现在被视为病理性的，无论其频段如何，尽管可能难以将它们与在相似频率范围内出现的生理性HFOs区分开来。发作间期的HFOs可能大多局限于发作起始区，从而为其定位提供了一种新方法。更重要的是，多项研究已将HFOs与潜在的致痫性联系起来，表明HFOs可作为该疾病的潜在生物标志物。除了HFOs，发作期基线偏移（IBS；或直流偏移）和超低频活动（ISA）（ISA：<0.1Hz）的分析也引起了关注。研究表明：IBS可使用具有长时间常数的常规交流放大器记录；IBS在传统EEG发作时出现，但与传统频率相比，其空间分布受限；在切除术中纳入IBS电极触点可能与良好的癫痫发作结果相关。只有少数研究在同一患者组中对所有EEG频率进行了综合评估。后一项研究表明，发作起始区最好通过发作期HFOs定位，IBS往往能提供更广泛的定位，而传统频率可能无法定位。然而，这些研究纳入的患者数量较少，无法就基于选择性或联合切除HFO、IBS和CFA电极触点的术后癫痫发作结果得出明确结论。需要开展大规模、最好是前瞻性的研究，以进一步评估不同EEG频率在癫痫中的意义。
