Physiological and pathological high frequency oscillations in focal epilepsy
Jan Cimbalnik1,2, Benjamin Brinkmann1,3, Vaclav Kremen1,3,4
1Mayo Systems Electrophysiology Laboratory Department of Neurology Mayo Clinic 200 First St SW Rochester Minnesota 55905.
Annals of Clinical and Translational Neurology
|September 26, 2018
Summary
High-frequency oscillations (HFOs) are biomarkers of epileptogenic brain tissue. Differentiating pathological HFOs from physiological ones remains challenging, but classifying tissue under electrodes is feasible and aids surgical outcomes.
Area of Science:
- Neuroscience
- Epilepsy Research
- Biomarker Discovery
Background:
- High-frequency oscillations (HFOs) are increasingly recognized as potential biomarkers for identifying the epileptogenic zone in epilepsy.
- Clinical translation of HFOs is hindered by challenges in distinguishing pathological HFOs (pathHFO) from physiological HFOs (physHFO) and classifying tissue under electrodes.
Purpose of the Study:
- To investigate HFOs (65-600 Hz) as biomarkers of epileptogenic brain.
- To address barriers in clinical translation: distinguishing pathHFO from physHFO, classifying epileptogenic tissue, and ensuring result reproducibility.
Main Methods:
- Intracranial EEG (iEEG) was recorded in 90 epilepsy patients and 11 controls.
- HFOs were detected using validated algorithms; physHFOs were induced via cognitive/motor tasks in nine epilepsy patients.
- A support vector machine (SVM) was developed to classify tissue under electrodes as normal or epileptogenic using HFO features.
Main Results:
- Significant overlap existed between spontaneous physHFO, task-induced physHFO, and pathHFO, but pathHFO amplitudes were higher (P < 0.0001).
- High gamma pathHFO showed the strongest association with the seizure onset zone (SOZ), elevated in 70% of epilepsy patients (P < 0.0001).
- Failure to resect high gamma pathHFO-generating tissue correlated with poor surgical outcomes (P < 0.0001). An SVM achieved 63.9% sensitivity and 73.7% specificity in classifying epileptogenic electrodes.
Conclusions:
- A wider range of interictal pathHFOs (65-600 Hz) are biomarkers of epileptogenic brain, linked to SOZ and surgical success.
- Distinguishing between physiological and pathological HFOs remains difficult.
- Classification of tissue under individual electrodes as epileptogenic is feasible, with open-source data and algorithms provided for future research.
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