Neurology and Therapeutics

Scalp Electroencephalogram (EEG) recording is first step in the evaluation of patients being considered for Epilepsy Surgery. Most of these patients have undergone more than one EEG recording and due to intractable seizures are being considered for epilepsy surgery. The yield of a routine first EEG record is usually 40-50% which however, after the third to fourth EEG increases to up to 80%. Overall, standard EEG with 10–20 system provides limited coverage of the temporal regions detecting only about 58% of temporal spikes or interictal epileptiform discharges (IEDs) in temporal lobe epilepsy (TLE). Additional electrodes help in increasing this yield including zygomatic, mandibular notch, nasopharyngeal (NP), sphenoidal (SP), and foramen ovale (FO) electrodes also help similarly. Preoperative interictal EEG abnormalities commonly observed in TLE are focal arrhythmic slowing (either theta or delta) and focal IEDs that are often restricted to the anterior temporal areas. In majority, these abnormalities correlate well with seizure onset zone and the structural abnormalities seen on magnetic resonance imaging (MRI). In TLE, single or serial outpatient EEGs demonstrate strong correlation of interictal abnormalities with areas of surgical resection and postoperative seizure outcomes (90% for IEDs and 82% for focal slowing). Such strong correlations may obviate the need for mandatory ictal recordings during presurgical workup in patients with unilateral hippocampal atrophy (HA) and congruent clinical and neuropsychological data, However, ictal recording becomes essential to rule out the possibility of concurrent psychogenic nonepileptic seizures (PNESs). Moreover, bilateral TLE, coexisting extratemporal epilepsy, or generalized epilepsy. A number of illustrative cases will be reviewed.