Abstracts

Rationale: Multiple subpial transections (MST) are often used to manage intractable epilepsy for seizure foci located in eloquent cortex. Long term outcome data is not available. Our review of a large MST cohort reveals long term prognosis. Methods & Results: 65 patients underwent usual evaluation & all underwent invasive monitoring & cortical mapping identifying primary motor/sensory or language cortex. MST was used because the seizure focus was found to coincide with eloquent areas. 5 had MST alone, 60 had the seizure foci at least partially localized to non-eloquent cortex & underwent both resection & MST. Follow up averaged 40 months (range: 6-89 months. Modified Engel outcome scale was used (Grade I = no seizure, auras or inconsequential simple partial events; II = marked reduction with rare disabling events; III = > 50% reduction; IV = no change). Grade I was achieved in 40%, Grade II in 12.3%, Grade III in 29.2%, & Grade IV in 18.5 %. Several patterns were recognized: 2 (3.1%) had a higher frequency of seizures in immediate post-operative period and settled into lower seizure frequency; 47 (72.3%) achieved long-term seizure pattern within one year, regardless of eventual grade; significant worsening of seizures in 16.5% (11/65) between 2 & 5 years post-op. 5 of 11with late worsening still were Grade I at 2 years; 4 regressed to Grade III & 1 regressed to Grade IV. 5/6 Grade II outcomes at 2 years deteriorated to Grade III, & to Grade IV in 1. Patients with progressive pathology (e.g. new or worsening tumor) were excluded from analysis. Discussion: MST are beneficial: > 80% had long-term significant reduction in seizure frequency (Grades I to III), & > 53% either entirely or virtually seizure-free. 84% achieved long-term seizure frequency within 2 years, & remainder suffered increased seizure frequency between years 2 & 5. Compared to published efficacy reports our findings (after a longer follow-up period) reflects the presence of a subgroup of regressors whose seizure frequency increased several years after surgery. Etiology and comparison with reported efficacy are discussed.