A historical cohort of temporal lobe surgery for medically refractory epilepsy: a systematic review and meta-analysis to guide future nonrandomized controlled trial studies

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OBJECTIVE

Recent trials for temporal lobe epilepsy (TLE) highlight the challenges of investigating surgical outcomes using randomized controlled trials (RCTs). Although several reviews have examined seizure-freedom outcomes from existing data, there is a need for an overall seizure-freedom rate estimated from level I data as investigators consider other methods besides RCTs to study outcomes related to new surgical interventions.

METHODS

The authors performed a systematic review and meta-analysis of the 3 RCTs of TLE in adults and report an overall surgical seizure-freedom rate (Engel class I) composed of level I data. An overall seizure-freedom rate was also collected from level II data (prospective cohort studies) for validation. Eligible studies were identified by filtering a published Cochrane meta-analysis of epilepsy surgery for RCTs and prospective studies, and supplemented by searching indexed terms in MEDLINE (January 1, 2012–April 1, 2018). Retrospective studies were excluded to minimize heterogeneity in patient selection and reporting bias. Data extraction was independently reverified and pooled using a fixed-effects model. The primary outcome was overall seizure freedom following surgery. The historical benchmark was applied in a noninferiority study design to compare its power to a single-study cohort.

RESULTS

The overall rate of seizure freedom from level I data was 72.4% (55/76 patients, 3 RCTs), which was nearly identical to the overall seizure-freedom rate of 71.7% (1325/1849 patients, 18 studies) from prospective cohorts (z = 0.134, p = 0.89; z-test). Seizure-freedom rates from level I and II studies were consistent over the years of publication (R2 < 0.01, p = 0.73). Surgery resulted in markedly improved seizure-free outcomes compared to medical management (RR 10.82, 95% CI 3.93–29.84, p < 0.01; 2 RCTs). Noninferiority study designs in which the historical benchmark was used had significantly higher power at all difference margins compared to using a single cohort alone (p < 0.001, Bonferroni’s multiple comparison test).

CONCLUSIONS

The overall rate of seizure freedom for temporal lobe surgery is approximately 70% for medically refractory epilepsy. The small sample size of the RCT cohort underscores the need to move beyond standard RCTs for epilepsy surgery. This historical seizure-freedom rate may serve as a useful benchmark to guide future study designs for new surgical treatments for refractory TLE.

ABBREVIATIONS AED = antiepileptic drug; ATL = anterior temporal lobectomy; ERSET = Early Randomized Surgical Epilepsy Trial; RCT = randomized controlled trial; ROSE = Radiosurgery or Open Surgery for Epilepsy; RR = risk ratio; SAH = selective amygdalohippocampectomy; SLATE = Stereotactic Laser Ablation for Temporal Lobe Epilepsy; SRS = stereotactic radiosurgery; TLE = temporal lobe epilepsy.

Article Information

Correspondence Edward F. Chang: University of California, San Francisco, CA. edward.chang@ucsf.edu.

INCLUDE WHEN CITING Published online June 28, 2019; DOI: 10.3171/2019.4.JNS183235.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Flowchart for study selection.

  • View in gallery

    Forest plot of meta-analysis result. Effect size is shown as RR with 95% CI reflecting likelihood of seizure-free outcome for ATL surgery over medical management and SRS. M–H = Mantel-Haenszel. Figure is available in color online only.

  • View in gallery

    Graph showing historical trend of adult seizure-freedom rates in prospective and RCT TLE studies. Each data point represents 1 study, with seizure freedom (at least Engel class Ib) after TLE surgery plotted against year of publication. A linear regression (dotted line) indicates consistent TLE outcomes across time (R2 < 0.01, p = 0.73).

  • View in gallery

    Graph comparing the power of the historical benchmark to a single-study cohort in detecting noninferiority. The solid lines represent the power to detect noninferiority from using the historical benchmark at varying treatment arm sizes (x axis). The dotted lines are the power from using the Wiebe cohort alone. Each color represents different noninferiority margins (blue, 0.05; green, 0.10; red, 0.15). Figure is available in color online only.

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