Systematic review of outcomes and endpoints in preventive migraine clinical trials.

BACKGROUND: Over the last six decades (earliest included publication from 1959), clinical trials of migraine preventive treatments have led to the regulatory approval of many medications and devices. Despite similar clinical goals, the outcomes and endpoints used in these trials are broad and not well standardized. OBJECTIVE: To describe results from a systematic literature review focused on outcomes and endpoints used in preventive migraine clinical trials. METHOD: A systematic literature review, following a pre-specified (unregistered) protocol developed to adhere to recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, was conducted to characterize the endpoints and outcomes used in preventive migraine clinical trials. Predetermined terms were searched in PubMed on October 28, 2019. Data related to trial design, subject characteristics, outcomes, and endpoints reported in each publication were extracted. Descriptive summaries of these features were tabulated for the recent subset of publications, published during or after 1988, that were randomized, blinded, and focused on pharmacological or device therapies for the preventive treatment of migraine. RESULTS: The initial literature search identified 1506 publications, of which 757 publications were eligible for data extraction. Of specific clinical interest were the recent subset of 268 articles (268/757, 35.4%) fulfilling the targeted criteria. Results showed that the outcomes used to define endpoints varied substantially across publications. For example, in the recent subset of publications, 68.7% (184/268) of the publications examined ≥1 migraine-specific outcome, 39.6% (106/268) examined ≥1 headache-specific outcome, 50.7% (136/268) examined ≥1 acute/rescue medication use outcome, 40.3% (108/268) examined ≥1 headache-related patient-reported outcome measure (PROM), and 22.0% (59/268) examined ≥1 non-headache-specific PROM. Furthermore, the definition of the endpoints used (e.g., change from baseline, fixed timepoint comparisons, categorization of "responders" to treatment based on wide variety of "responder definitions") also differed across publications. CONCLUSION: Publications from clinical trials of preventive migraine pharmacologic and device treatments differed in terms of study design, endpoint definitions, and how endpoints and outcomes were measured. Although there were common outcomes and endpoints used across publications, no clear "standardized" set of endpoints and outcomes emerged. The inconsistencies in endpoints and outcomes within this literature suggest that the development of a uniform set of outcomes and endpoints could improve the clinical meaningfulness of clinical trial results, facilitate cross-trial comparisons and better inform patient care. This standard set of outcomes and endpoints should be statistically robust and informed by the priorities of various stakeholders, most importantly, the needs and preferences of people living with migraine.