Abstracts

Rationale:
Patients with medically refractory focal epilepsy who have had adequate trials of two or more antiepileptic drugs (AEDs) are recommended to undergo multiple testing modalities to assess candidacy for epilepsy surgery by attempting to localize ictal onset zone(s). Potentially causative lesions on magnetic resonance imaging (MRI) help guide the surgical plan and lesional patients may or may not require intracranial electroencephalography (iEEG) for further localization prior to proceeding to surgery. For patients without MRI lesions, iEEG electrode placement must be guided by scalp EEG, ancillary imaging studies and clinical data. The absence of a potentially causative lesion on pre-operative imaging is considered a poor prognostic factor. In patients treated with responsive neurostimulation (RNS) the presence of a structural lesion on MRI has been shown in some studies to be predictive of a better response to treatment, possibly due to more accurate localization of seizure onset, although contrasting reports exist in the literature.
Method:
The medical records of 20 patients who received iEEG-guided RNS implantation between the years of 2015 and 2019 at our institution were reviewed. We compared demographic characteristics and outcomes of RNS therapy among patients with and without epileptic lesions on MRI. Only patients with 6 months of available follow up were included for analysis.
Results:
Patient characteristics and outcomes are shown in Table 1. Nonlesional patients were younger at the time of surgery than lesional patients and had more available clinical follow up. The magnitude of the reduction in monthly seizure frequency at most recent follow up was not significantly different between nonlesional and lesional patients (-5.83 ± 15.35 in nonlesional, -12.36 ± 26.75 in lesional; p=0.525). There were no statistical differences in the reduction of dosage or number of anti-epileptic drugs between nonlesional and lesional patients.
Conclusion:
In a small retrospective examination of outcomes and characteristics among patients with medically refractory focal epilepsy, there was no significant difference in the degree of seizure reduction or medication reduction between nonlesional and lesional patients. The small sample size may limit the validity of these results. A time-dependent difference between these two groups may be missed in this study because of the short duration of follow up.  It should be noted that our sample included only patients who got iEEG prior to RNS placement, although there were some patients at our institution who did not receive iEEG before RNS placement surgery. Patients without epileptic lesions on MRI were younger at the time of surgery than patients with lesions. This may suggest that RNS should be considered earlier as a treatment choice for patients with lesions. More information is needed to determine if the presence of an epileptic lesion on MRI should be used for prognostication or patient selection when considering RNS for the treatment of medically refractory focal epilepsy.
Funding:
:None