Falsely localizing ictal onsets with depth EEG telemetry during anticonvulsant withdrawal

Area of Science:

• Neurology
• Neurosurgery
• Epileptology

Background:

• Surgical evaluation for epilepsy often involves chronic depth electrode recordings to precisely localize seizure origins.
• Anticonvulsant drug withdrawal is a common practice during evaluation to provoke habitual seizures for accurate localization.

Observation:

• A patient undergoing evaluation for partial complex seizures exhibited falsely localizing ictal onsets during phenytoin reduction.
• These atypical seizures appeared to originate from the contralateral temporal lobe, differing from the patient's habitual seizures.
• Four additional patients with anterior temporal lobectomies also had stereotactic electroencephalography (SEEG)-recorded contralateral seizure onsets, yet benefited from surgery.

Findings:

• Falsely localizing ictal onsets during anticonvulsant withdrawal, potentially due to drug reduction or electrode irritation, can mislead localization.
• A patient with falsely localizing onsets underwent surgery based on other findings, revealing an unsuspected tumor and resulting in sustained seizure freedom.
• Multifocal SEEG-recorded ictal onsets are generally a poor prognostic indicator, but atypical seizures during drug withdrawal may not predict postoperative seizure recurrence.

Implications:

• Atypical seizure onsets during drug withdrawal should be interpreted cautiously and not solely used to disqualify patients from epilepsy surgery.
• Careful consideration of all diagnostic data, including the nature of seizures and underlying pathology, is crucial for surgical candidacy.
• Successful surgical outcomes are possible even in the presence of some contralateral or atypical seizure activity during the evaluation phase.