Objective:The definition of drug-resistant epilepsy (DRE) affects case identification and treatment, and impacts prevalence or incidence estimates and health burden estimation in epidemiology. The objective of this systematic review is to evaluate the consistency between definitions of DRE in the literature and the official definition in the International League Against Epilepsy (ILAE) guidelines, and to estimate the incidence, prevalence, and risk factors for DRE. Methods: MEDLINE and EMBASE were searched for observational studies of DRE published between January 1980 and July 2015. The definitions of DRE in these studies were compared with the definition in the ILAE guidelines. Randomeffect model meta-analyses were used to generate pooled estimates of prevalence or incidence and pooled odds ratios of the association with risk factors. Results: Thirty-five studies met inclusion criteria, including 13 080 epilepsy patients and 3941 patients with DRE. The definition of DRE varied widely across studies, with only 12% meeting the requirements of the ILAE definition. The pooled prevalence proportion of DRE among epilepsy patients was 0.30 (95% confidence interval [CI] 0.19-0.42), and the pooled incidence proportion was 0.15 (95% CI 0.11-0.19). Age at onset, symptomatic epilepsy, abnormal neuroimaging findings, abnormal electroencephalography results, history of mental retardation, neuropsychiatric disorders, febrile seizure, and status epilepticus increased risk for DRE. Significance: There are limited high-quality data available on DRE. Lack of consistency in definitions limits the ability to obtain robust estimates on the burden of DRE. More data based on the ILAE definition from well-designed epidemiologic studies are needed to generate accurate and reliable results. K E Y W O R D Sdrug resistant, epidemiology, epilepsy, frequency, review, risk

Objective: Head-to-head randomized controlled trials (RCTs) are the gold standard for assessing comparative treatment effects. In the absence of direct comparisons between all possible antiepileptic drugs (AEDs), however, clinical decision-making in focal (partial onset) epilepsy relies on alternative evidence borne from indirect comparisons including network meta-analyses (NMAs) and from real-world evidence (RWE) studies. We review NMAs and observational RWE studies comparing AEDs in the adjunctive setting to compare the robustness of these methods and to formulate recommendations for future evidence development. Methods: A literature review identified NMAs and RWE studies comparing AEDs for the adjunctive treatment of focal seizures published between January 2008 and October 2018. NMAs were evaluated for robustness using a framework based on guidelines from the National Institute for Health and Care Excellence Decision Support Unit and the International Society for Pharmacoeconomics and OutcomesResearch. RWE studies were evaluated using the GRACE checklist. Results: From a total of 1993 records, 11 NMAs and six RWE studies were eligible. Key limitations identified in the NMAs include nonsystematic selection of RCTs, unexplored heterogeneity between included RCTs in terms of study and patient characteristics, and selection of AEDs and AED doses or dosing strategies that are not reflective of clinical practice. The main limitations of RWE studies concern sample size, design, and analysis methods. Approximately 90% of comparisons between individual AEDs were nonsignificant in the NMAs. None of the RWE studies adjusted for baseline differences between comparator groups; therefore, they lack the validity to make comparative conclusions. Significance: Current NMAs and RWE studies provide only nominal comparative evidence for AED treatments in focal epilepsy, and should be used with caution for decision-making due to their methodological limitations. To overcome these hurdles, adherence to methodological guidelines and concerted efforts to collect relevant outcome data in the real world are needed. |

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