Understanding Epilepsy Networks and Rapid White Matter Propagation of Epileptogenicity Through Interictal EEG
Naseem Zomorodi1, Patrick Hartnett1, Howard Goodkin1, Ifrah Zawar1
1University of Virginia
Background:
Because of its extensive connectivity, the parietal lobe epilepsies (PLE) can be difficult to localize. We provide an important example emphasizing the need to consider interictal epileptiform discharges (IEDs) in the multi-modal localization of the epileptogenic zone (EZ), further emphasizing the need to recognize epilepsy as a network disease that propagates through white matter tracts.
Results:
An 18-year-old male with drug resistant epilepsy (DRE) underwent presurgical evaluation for seizures consisting of behavioral arrest, left head turning, left gaze deviation with secondary generalization. Prior to admission, a right frontal lobe epilepsy was presumed based on seizure semiology and the presence of IEDs with a phase reversal in the right frontal region. During the presurgical evaluation, seizure video analysis demonstrated a subtle nystagmus prior to left gaze deviation and generalization. On detailed IED analysis, a posterior-to-anterior time lag with an initial spike component over the right parieto-occipital lobe followed by frontal lobe was appreciated. Further, a voxel-based morphometry (VBM) analysis of his brain MRI identified a lesion in the right superior parietal lobe (SPL), PET showed hypometabolism corresponding to VBM lesion, and magnetoencephalography (MEG) showed dipoles over the right parietal lobe concordant with VBM lesion. Stereo-EEG implantation confirmed an epileptogenic zone (EZ) in the right SPL with rapid spread to frontal lobe. Right SPL EZ was successfully ablated with laser.
Conclusions:
The slight delay between parietal and frontal involvement is likely due to rapid white matter propagation via the superior longitudinal fasciculus, highlighting the utility of IEDs in understanding the brain connectivity and rapid propagation of epileptogenicity through white matter tracts. This case also underscores the significance of a comprehensive multi-modal approach using clinical semiology, interictal and ictal EEG, VMB, PET, and MEG in epilepsy localization, especially in difficult to localize and deceptive non-lesional PLEs.