Quantitative EEG signatures in patients with and without epilepsy development after a first seizure

Objective: Diagnosing epilepsy after a first unprovoked seizure in the absence of visible epileptogenic lesions and interictal epileptiform discharges (IED) in the electroencephalogram (EEG) is challenging. Quantitative EEG analysis and functional connectivity (FC) have shown promise in identifying patterns across epilepsy syndromes. Hence, we retrospectively investigated whether there were differences in FC (imaginary part of coherency) and spectral band power in non-lesional, IED-free, unmedicated patients after a first unprovoked seizure in contrast to controls. Further, we investigated if there were differences between the patients who developed epilepsy and those who remained with a single seizure for at least 6 months after the first seizure. Methods: We used 240 s of resting-state EEG (19 channels) recordings of patients (n = 41) after a first unprovoked seizure and age and sex-matched healthy controls (n = 46). Twenty-one patients developed epilepsy (epilepsy group), while 20 had no further seizures during follow-up (single-seizure group). We computed source-reconstructed power and FC in five frequency bands (1 +/- 29 Hz). Group differences were assessed using permutation analysis of linear models. Results: Patients who developed epilepsy showed increased theta power and FC, increased delta power, and decreased delta FC compared to healthy controls. The single-seizure group exhibited reduced beta-1 FC relative to the control group. In comparison with the single-seizure group, patients with epilepsy demonstrated elevated delta and theta power and decreased delta FC. Significance: Source-reconstructed data from routine EEGs identified distinct network patterns between non-lesional, IED-free, unmedicated patients who developed epilepsy and those who remained with a single seizure. Increased delta and theta power, along with decreased delta FC, could be a potential epilepsy biomarker. Further, decreases in beta-1 FC after a single seizure may point toward a protective mechanism for patients without further seizures. Plain Language Summary: After a first seizure, some people develop epilepsy, while others do not. We looked at brain activity in people who had a seizure but showed no clear signs of epilepsy. By comparing those who later developed epilepsy to those who did not, we found that certain slow brain wave patterns (delta and theta) might indicate a higher risk of developing epilepsy. This could help doctors identify high-risk patients sooner.