Abstracts

Rationale:

Rationale:
The role of seizure spread between mesial temporal lobes (MTL) in bitemporal epilepsy is not well understood.  We looked at the characteristics of seizure spread frequency and timing of seizure spread and their possible relationship to clinical outcomes in RNS System bilateral MTL patients.
Method:
Methods:  Retrospective chart and ECoG review was performed on all RNS System patients with bilateral MTL depth leads implanted along the long axis of each hippocampi at 2 centers: California Pacific Medical Center and Yale.  Demographics, epilepsy history, baseline clinical seizure frequency, year 1 and 2 post-op clinical seizure frequencies (averaged over prior 3 months) were collected.  An epileptologist reviewed ECoGs of the last electrographic seizure each month or 24 seizures per patient over the first 2 years post-implant.  Seizures were classified by onset pattern, whether presence of spread to the opposite MTL, and spread time.  A Spearman correlation analysis was performed to determine relationships between seizure spread frequency or spread time and clinical outcome. A Chi square test was used to determine association between onset pattern and clinical outcome.
Results:
Results:  Twenty-three patients were implanted with RNS Systems with bilateral MTL leads over 10 years.  Demographics and epilepsy history can be found in Table 1.  The median % clinical seizure frequency reduction at year 1 (n=23) was 49% (mean: 49%, range: 20%-100%). Fourteen percent were seizure free at year 1.  The median % reduction at year 2 (n=18) was 65% (mean: 64%, range: 0-100%). Twenty-two percent (4/18) were seizure free at year 2. Eighty-three percent of all patients (n=19) had seizures spread to the opposite MTL.  In those patients, seizures spread in a median frequency of 30% of ECoGs (mean: 38%, range: 4-95%).  The median spread time was 23.8s (mean: 28s, range: 3.6-84s).  17% (n=4) had seizures that never spread between MTLs.  The seizure spread frequency or spread time did not significantly correlate with clinical seizure frequency reductions at year 1 (freq corr= -0.028, spread corr= -0.22) or year 2 (freq corr=+0.21, spread corr= -0.063).  A majority of patients (61%) had low-voltage fast activity as their seizure onset pattern versus a variety of other patterns (39%); there was no discernable association between onset pattern and response to RNS system treatment (p=0.26).
Conclusion:
Conclusion:  The RNS System was found to be effective in patients with bilateral hippocampal treatment at years 1 and 2 post-op.  The seizure onset pattern, frequency of seizure spread and rapidity of seizure spread did not appear to influence clinical outcome.
Funding:
:There was no funding for this abstract.