Abstracts

Rationale: Drop attacks are malignant epileptic seizures leading to significant injuries and morbidity. Such seizures are thought to arise from sudden bilateral synchronization of motor and premotor cortex. One strategy to control the sudden falls is to section callosal fibers in an attempt to disrupt synchronized discharges. Because it has been shown that motor and premotor fibers cross in the posterior half of the corpus callosum (CC), a novel surgical strategy is to selectively section the posterior half of the CC, therefore sparing prefrontal fibers. Although this strategy has been shown to be both effective and superior to anterior sections to control drop attacks, no study has analyzed if section of the posterior CC while sparing the anterior half leads to diminished secondary synchronization. Our aim is to study the rate of epileptic discharges and, especially, bilateral secondary synchronization, in patients undergoing selective posterior callosotomy. Methods: Pre- and post-section EEGs of a random sample of 12 unselected patients with refractory drop attacks who underwent selective posterior callosotomy at the Porto Alegre Epilepsy Center were analyzed in detail. All had been previously discussed in a multidisplinary conference and underwent high resolution MRI and prolonged Video-EEG (pre and post-callosotomy). Pre- and post-surgical Video-EEG lasted for at least 24 hours. 24 hour - recordings were visually analyzed and the following variables quantified: (i) number, rate and pattern of electrographic and clinical seizures, (ii) absolute number and rate of bi-synchronous discharges, (iii) regionalization of discharges and (iv) morphology of epileptic discharge. In addition, we analyzed changes in the background rhythms. Pre- and post-operative recordings were compared through Wilcoxon Rank Sum Test. Results: Mean age at surgery was 18.8 ± 12.2 years and eight patients were female. Secondary bilateral synchrony (SBS) decreased from 2122 ± 3.897.75 to 2 ± 298.75 (p= 0.002; Wilcoxon). Generalized EEG seizures significantly reduced post-surgically (62 ± 177 x 1 ± 7.5; p=0.002, Wilcoxon). Tonic seizures during sleep and rate of burst suppression also decreased (p=0.01 and 0.028, respectively). There was no significant change in relation to localization of discharges, morphology or background rhythms. Conclusions: Posterior callosotomy is a highly effective surgical treatment for drop attacks and greatly improves electroencephalographic patterns post-surgically. As demonstrated by our study, post-surgical EEG showed significantly less synchronized discharges (even focally) and generalized EEG seizures. Further studies may analyze if such changes in epileptogenicity lead to improve cognition and a switch from pathogenic to healthy networks dynamics. Funding: No funding