Abstracts

Rationale: Significant discrepancies exists in the management of patients with apparent bitemporal epileptogenicity after scalp monitoring (SEM) evidenced by bilateral independent ictal patterns (IPs), interictal epileptiform discharges (IEDs) or unilateral or nonlocalizing IPs or IEDs associated with discordant presurgical data. This study examined the ability of scalp IPs and IEDs to predict candidacy for temporal lobe resection and outcome in cases that required intracranial EEG monitoring (IEM). Methods: The Henry Ford Hospital electronic database was reviewed to identify adults who had IEM with bitemporal electrode placement. Patients were categorized according to ictal patterns on SEM into two main groups: I, unilateral (UL) IPs and II, bilateral (BL) IPs. Each group was further subdivided according to IED findings: A, UL/ipsilateral (IL) IEDs with discordant ancillary data; B, BL IEDs; C, nonlocalizing IEDs. An additional category D was found in UL IP group with contralateral (CL) IEDs. On the basis of SEM findings, patients who proceeded to surgery after IEM were grouped subsequently as: I, exclusively concordant IL epileptogenicity; II, IL preponderant (>75% of IPs) in BL epileptogenicity; III, CL preponderant (>75% of IPs) in BL epileptogenicity; IV, approximately equal (~50% IPs) in BL epileptogenicity. Outcome measures included (i) the decision for epilepsy surgery based on IEM and (ii) the rate of favorable seizure outcome (Engel class IIB and above). Descriptive statistics were applied to test for correlation between IEM and SEM findings and favorable outcomes. Results: Ninety-three patients (40F, 53M) with median age, 45y (15-74y) and median age at epilepsy onset, 9y (0-56y) were accrued. In the surgery group, median age at surgery was 37y (9-56y) and the median postoperative followup was 42m (7-184m). Lateralization according to IEM provided reliable outcome prediction (p<0.001) for TL resections (Table 1). Outcomes in 30 patients not proceeding to resection are reported in Table 2. Conclusions: Intracranial EEG monitoring with bitemporal electrode implantation is essential in cases of putative bitemporal epileptogenicity. There appears to be a trend towards better outcome with unilateral ictal patterns and interictal epileptifrom discharges despite other discordant nonelectrographic presurgical data. The presence of bilateral ictal patterns and/or interictal epileptiform discharges is associated with less favorable outcomes.