The localizing value of focal delta slowing in temporal lobe epilepsy

Background: Clinical and structural correlates of lateralized interictal delta activity in patients with temporal lobe epilepsy (TLE) have been well documented in the literature. Nevertheless, its occurrence has not been considered a significant clinical feature. Objective: To evaluate the significance of focal delta- range slowing for localizing the epileptogenic focus in patients with TLE, and predicting the outcome of temporal lobe surgery. Methods: Sixteen consecutive patients with temporal lobe epilepsy who underwent anterior temporal lobe resections were selected for the study. Findings of MRI, SPECT, neuropyschology assessment, pathology and surgical outcome were analyzed and correlated with focal delta slow activity of background rhythm. Results: Twelve of 16 patients (75%) had localized temporal delta slowing corresponding to the resection site and pathology. Temporal delta slowing was the most frequent interictal EEG finding (75%) compared to spike and sharp wave (44%). MRI showed concordant abnormalities in 75% of the patients, and neuropyschology testing was able to lateralize the involved hemisphere in 37.5%. SPECT was concordant in 56%. There was no false localization with temporal delta activity. Slow wave EEG had a higher marginal probability than neuropsychological assessment of predicting the focus, and was equally effective as other investigative methods. Conclusion: These results suggest that focal temporal delta slowing is useful in the localization of epileptogenic foci. There was no discordance with the resection site and pathology.