Abstracts

Rationale: Patients with mesial temporal lobe epilepsy and bilateral MRI evidence of Mesial Temporal Sclerosis (Bilateral MTLE-HS) present considerable challenges during presurgical evaluation. Whether they resemble those with unilateral MTLE-HS at presentation is unknown. We looked into the clinical and electrical data of patients with Bilateral MTLE-HS and tried to identify features if any, which could differentiate them from Unilateral MTLE-HS. Methods: We reviewed the clinical and electrical data of 29 consecutive patients who presented with Bilateral MTLE-HS to our institute between 2006-2008. Those with extratemporal lesions on MRI, predominant extratemporal IEDs, extratemporal or pseudo temporal semiology were excluded. This was compared with similar data of 27 consecutive patients of Unilateral MTLE-HS who presented during the same study period and had undergone Anterior Temporal Lobectomy (ATL) with a minimum follow-up of 1 year and remained seizure free and aura free. All had pathological confirmation of MTS. 198 seizures in the bilateral group were compared with 100 seizures in the unilateral group. Results: Among the demographic variables, significant differences were observed in the Bilateral MTLE-HS group compared to Unilateral MTLE-HS in the following: history of meningoencephalitis (20% vs. 3.7%), history of status (17% vs. none), age at initial insult (4 years vs. 1 yr) and the subsequent latent period (6.3 years vs. 11 years). Regarding semiology, differences were observed in the presence of epigastric aura (20% vs. 48%), head turn (58% vs. 40%), tonic posturing (55% vs. 40%), history of falls (24% vs. 14%), history of clonic jerks (17% vs. 7%), presence of secondary generalization in more than 20% of seizures (24% vs. none), seizure frequency of more than 5/month during the previous year (52% vs. 22%) and history of clustering (65% vs. 25%). Clinical lateralization could be done in 85% of unilateral cases compared to 45% of bilateral cases. Regarding electrical data, significant differences were noted in the presence of behavioral arrest at onset (33% of seizures vs. 73%), clonic jerks (20% vs. 2%), bilateral lateralizing signs (30% vs. 14%), ictal theta (60% vs. 79%) and delta rhythm (15% vs. 4%),varying semiology(14/29 patients vs. 1/27),ictal onset contra lateral to the side of maximum involvement(21% of seizures vs. 3%) and switch of laterality or asynchronous temporal rhythm(17% vs. 10%). Conclusions: Bilateral MTLE-HS seems to be a distinct electro-clinical entity when compared to unilateral MTLE-HS.Antecedent history of meningoencephalitis or status epilepticus, clonic jerks and falls, higher seizure frequency and more frequent secondary generalization, lack of behavioral arrest, varying seizure semiology, presence of bilateral clinical signs in semiology and delta rhythm at ictal onset in an individual who presents with MTLE may be a pointer towards the presence of radiologic evidence of bitemporal involvement.