Abstracts

Rationale: Among temporal lobe epilepsy (TLE) a subgroup exists, represented by TLE with bilateral temporal lobe involvement during seizures, the bitemporal epilepsy (BTLE). Differently from unilateral TLE (UTLE), the anatomo-electro-clinical features of BTLE have not been clearly defined. BTLE patients do not represent good candidates for epilepsy surgery, hence they should be accurately identified. We aim to define the anatomo-electro-clinical features of a cohort of BTLE patients, identifying the main features differentiating them from UTLE. Methods: Among the subjects studied for pre-surgical evaluation, we identified 48 drug-resistant BTLE patients who underwent a long-term video-EEG monitoring (VEEG) and had seizures showing a bilateral temporal lobe involvement. We collected all the main electro-clinical and neuroimaging data of these patients (demographics, interictal and ictal EEG, ictal signs, brain MRI), comparing them to a group of 38 consecutive patients operated on for UTLE from 2005 to 2011 and seizure-free from at least 24 months. A p-Value <0.05 was considered significant for statistical analysis. Results: Two possible ictal discharge patterns were identified: (1) seizures simultaneously or sequentially involving the two temporal lobes, without the possibility to lateralize the seizure onset and its subsequent development (non-lateralized bitemporal seizures); (2) different seizures in the same patient alternatively arising from the two temporal lobes (independent bitemporal seizures). BTLE showed statistically significant differences as compared to UTLE. BTLE patients had older age at epilepsy onset (p=0.023), infrequent positive family history for epilepsy (p=0.042), more frequent bilateral asynchronous interictal epileptiform discharges (IEDs), both in wakefulness (p=0.03) and in sleep (p<0.001), bilateral upper limb dystonia (p=0.008) and auditory aura (p=0.032); on the other hand less frequently they had recognizable initial ictal EEG pattern (focal flattening or low-voltage fast activity, LVFA) (p<0.001), post-ictal memory of the seizures (p=0.001), staring (p=0.001), head deviation (p=0.004), oro-alimentary automatisms (p=0.009), positive brain MRI (p<0.001). Only BTLE patients had bilateral MRI alterations (hippocampal sclerosis) (p<0.001). Four out of 48 BTLE patients had been operated on, performing a right antero-mesial temporal resection. Seizure outcome was non-satisfactory for all of them, who belong to Engel Class III. Conclusions: Our data indicate the existence of a well recognizable BTLE phenotype that can be non-invasively differentiated from UTLE. The possibility to identify BTLE patients during the pre-surgical evaluation, or even to clinically suspect a bitemporal origin of seizures before VEEG, by identifying a peculiar anatomo-electro-clinical pattern, is an important diagnostic tool for the epileptologist, when evaluating a new patient, above all for a pre-surgical assessment. In our opinion BTLE subjects are not good candidates for resective surgery, and probably represent a large proportion of the bad outcome in TLE surgery.