Abstracts

Rationale: Callosotomy is a surgical therapeutical option for cases of medical refractory generalized epilepsy. The literature studying the contribution of neurophysiological data in the characterization of prognosis for these cases is scarce and inconclusive. We saught to quantify the evolution of epileptic activity (EA) in patients submitted to callosotomy while comparing them with the observed clinical evolution. Methods: The EA (spikes, spike-waves, sharp waves) for each hemisphere was quantified in a series of regular EEG recordings (prior to callosotomy, first 2 months and 6-12 months post-callosotomy) conducted in 4 patients submitted to anterior callosotomy within our Epilepsy Surgery group. The following indexes were calculated: 1) frequency - hemispherical epileptic activity per minute (spm), 2) lateralisation - ratio of epileptic activity quantified in each hemisphere (rH:h), 3) synchrony - fraction of the total epileptic activity coincident in both hemispheres in each epoch of 1s. The evolution in time for seizure type and frequency, and the changes in the number of anti-epileptic drugs and posology was recorded. Results: The baseline EEG recordings had a median frequency of epileptic activity of 47.4 spm, a median rH:h of 1.10 (I.1.01, II.1.09; III. 1.21; IV. 1.11) and a median coincident EA of 83.53%. After callosotomy, an increase in lateralisation was observed, with a median value of 1.43 (1.41, II. 1.19; III. 2.06; IV. 1.45) and 2.19 (I. 2.92, II. 1.18; III. 7.56; IV. 1.45) during the first 2 months and at 6-12 months, respectively. In terms of synchrony, a decrease along time was observed with a median value of 63.18% and 39.97% during the first 2 months and at 6-12 months, respectively. The frequency of EA did not change globally over time: median values of 21.69 (2 months) and 43.33 spm (6-12 months). Clinically, during the first year post-callosotomy, a reduction in seizure frequency was observed in all patients with remission of tonic-clonic and atonic generalised in patients I, III, IV. Patient II maintained these seizures types. Conclusions: In all patients, seizure frequency reduction was observed. The coincident reduction in synchrony of epileptic activity is in line with a previous study. The lack of remission of tonic-clonic and atonic generalised was coincident with smaller changes in the lateralization index. We interpret this fact as the existence of bilateral independent epileptic foci or the persistence of alternative pathways of generalization. Although, the small sample of the present study poses limitations, the perspective that patients with a less favorable response associate with the maintenance of a non-lateralised EA warrants further investigation. Conversely, the value of EA lateralisation post-callosotomy as a good prognosis factor should be studied.