Extratemporal epilepsies mimicking temporal mesial epilepsy.

Area of Science:

• Neurology
• Neurosurgery
• Epileptology

Background:

• Approximately 30% of patients with focal seizures exhibiting mesial temporal semiology continue to experience seizures post-anterior temporal resection.
• Unrecognized extratemporal seizure onset is a significant factor contributing to persistent seizures after surgery.
• Accurate localization of seizure onset is critical for effective epilepsy treatment.

Purpose of the Study:

• To investigate cases where clinical semiology suggested mesial temporal epilepsy but stereoelectroencephalography (SEEG) revealed extratemporal seizure origins.
• To highlight the limitations of non-invasive diagnostic methods in accurately identifying seizure onset zones in complex epilepsy cases.
• To emphasize the importance of SEEG in diagnosing drug-resistant epilepsy with atypical semiology.

Main Methods:

• Retrospective analysis of six patients with drug-resistant epilepsy and mesial temporal semiology from three tertiary care centers.
• Confirmation of seizure onset using stereoelectroencephalography (SEEG).
• Review of non-invasive investigations including video-electroencephalograms (EEG) and positron emission tomography (PET)-scans.

Main Results:

• SEEG identified extratemporal seizure onsets in all six patients initially suspected of having mesial temporal epilepsy.
• Five patients were diagnosed with mesial parietal epilepsy, and one with fronto-polar epilepsy upon SEEG confirmation.
• Non-invasive data were misleading in several cases, suggesting temporal lobe epilepsy or mesial parietal epilepsy, underscoring diagnostic challenges.

Conclusions:

• Clinical semiology alone can be deceptive, leading to misdiagnosis of mesial temporal epilepsy when the origin is extratemporal.
• Stereoelectroencephalography (SEEG) is essential for accurate localization in drug-resistant epilepsy cases where non-invasive methods are inconclusive.
• Prospective studies investigating the systematic use of specific electrodes in SEEG for non-lesional temporal lobe epilepsy are warranted.