Characterizing Demographic, Racial, and Geographic Diversity in Dementia Research: A Systematic Review.

Importance: For informed decision making on diagnosis and treatment of dementia, physicians and their patients rely on the generalizability of evidence from published studies to clinical practice. However, it is uncertain whether everyday care of elderly patients with dementia is sufficiently captured in contemporary research. Objective: To systematically review contemporary dementia research in terms of study and patient characteristics in order to assess generalizability of research findings. Evidence Review: PubMed was searched for dementia studies published in the top 100 journals in the fields of neurology and neuroscience, geriatrics, psychiatry, and general medicine between September 1, 2018, and August 31, 2019. Two reviewers extracted study characteristics, including setting, number of participants, age at diagnosis, and use of biomarkers. Findings: Among 513 identified studies, 211 (41%) included fewer than 50 individuals with dementia and were excluded. The remaining 302 studies included a median (interquartile range) of 214 patients (98-628) with a mean (SD) age at diagnosis of 74.1 years (8.0). Age at diagnosis differed with study setting. Patients in the 180 clinic-based studies had a mean (SD) age of 71.8 (6.4) years at time of diagnosis compared with 80.6 (4.7) years among patients in the 79 population-based studies (mean difference, 8.8 years; 95% CI, 7.3-10.2). Use of magnetic resonance imaging, positron emission tomography imaging, and cerebrospinal fluid imaging was mostly done in clinic-based studies (80% to 96%) and consequently in relatively young patients (mean [SD] age, 71.6 [5.1] years). A longitudinal design was more common in population-based studies than in clinic-based studies (82 % vs 40%). Most studies originated from North America and Europe (89%), including almost exclusively White participants (among 74 studies [22%] reporting on ethnicity: median [interquartile range], 89% [78-97]). The 3 most studied cohorts represented 21% of all included study populations. Conclusions and Relevance: Contemporary dementia research is limited in terms of racial and geographic diversity and draws largely from clinic-based populations with relatively young patients. Greater inclusivity and deeper phenotyping in unselected cohorts could improve generalizability as well as diagnosis and development of effective treatments for all patients with dementia.