Ictal Switch Pattern among TEMPORAL LOBE SEIZURES and its Association with Other Markers of Bilaterality - A Retrospective Multicentre Study from North Kerala.

BACKGROUND

Ictal switch in the temporal lobe is a rarely described phenomenon where ictal rhythm lateralized to one hemisphere shifts to the contralateral hemisphere and remains for a period of at least 10 seconds. It is important to recognize this electrographic event as it can indicate bilateral epileptogenicity, which is associated with poor surgical outcomes.

Objective

This study was aimed to determine the prevalence of ictal switch of lateralization on scalp electroencephalogram (EEG) during temporal lobe seizures and its relationship with interictal spike lateralization and Magnetic Resonance Imaging (MRI) abnormalities, as well as to ascertain the long-term seizure outcome in these patients.

METHODOLOGY: This retrospective observational study was conducted at two epilepsy centers in North Kerala over a period of three years from January 2022 to December 2024. Patients with temporal lobe seizures who underwent long-term video EEG monitoring for presurgical evaluation were included. All seizures recorded were analyzed to detect ictal switch of lateralization. Interictal data were organized on the basis of spike lateralization into those with unilateral or bilateral spikes.

RESULTS

Eight out of 265 patients (3%) demonstrated ictal switch. The mean age of onset was 13.9 years, and the mean duration was 17.18 years. All patients had bilateral interictal epileptiform discharges (IEDs). Five patients exhibited 70% or more IEDs lateralized to one hemisphere. MRI showed unilateral involvement in four patients and bilateral involvement in one patient. Two patients (25%) were seizure-free on three anti-seizure medications on follow-up.

CONCLUSION

Ictal switch of lateralization is an atypical and rare observation in patients with temporal lobe epilepsy (TLE). Its presence heightens the likelihood of bilateral epileptogenicity in the presence of other markers of bilateral involvement such as bilateral interictal discharges or bilateral radiological findings.