We investigated 109 patients who received anterior temporal lobectomy for intractable mTLE by post-operative follow-up for at least 11/2 years. We reviewed pre-operative 2-hour interictal EEGs, counted interictal epileptiform discharges (IEDs), and compared the lateralization of IEDs with the side of surgery and surgical outcome. Twenty of 22 patients who had no spikes and 44 of 51 who had unitemporal spikes became seizure free after surgical resection. The correct lateralization of the epileptogenic side was possible in 90. 9% of the patients with unitemporal IEDs. In 12 seizure-free patients of 15 patients with less than 70% predominance of IED in one temporal lobe, the positive predictive value of the lateralization was 41.7%. In 16 seizure-free patients of 21 with more than 70% preponderance of IED in one lobe, the positive predictive value was 81.3%. Surgical outcome of patients with unitemporal and bitemporal IEDs were not significantly different. Interictal scalp EEG can be used as a lateralizing tool in mTLE when the temporal IEDs appear with more than 70% preponderance in one side. Although the presence of bitemporal IEDs often causes confusion in terms of the correct lateralization, it does not affect the surgical outcome.
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