Representativeness of European clinical trial populations in mild Alzheimer's disease dementia: a comparison of 18-month outcomes with real-world data from the GERAS observational study

Background: Comparison of disease progression between placebo-group patients from randomised controlled trials (RCTs) and real-world patients can aid in assessing the generalisability of RCT outcomes. This analysis compared outcomes between community-dwelling patients with mild Alzheimer's disease (AD) dementia from two RCTs (pooled European (EU) data from EXPEDITION and EXPEDITION 2) and similar patients from the EU GERAS observational study. Methods: Data from placebo-group patients with mild AD dementia from the RCTs (EU countries only) were compared with data from GERAS patients with mild AD dementia. Between-group differences for changes over 18 months were analysed for cognition, functioning, neuropsychiatric symptoms, health-related quality of life (HRQoL) and caregiver time using propensity score-adjusted models. A sensitivity analysis compared EU/North American (EU/NA) EXPEDITION patients with GERAS patients. Results: EU EXPEDITION patients (n = 168) were younger than GERAS patients (n = 566) (mean (standard deviation, SD) age 71.9 (7.4) versus 77.3 (6.9) years; p < 0.001) and were more likely to use AD treatment (95% versus 84%; p < 0.001). Cognitive performance was similar at baseline in both populations, although GERAS patients showed greater functional impairment (p = 0.005) and lower HRQoL (p < 0.05). At 18 months, no statistically significant differences between EXPEDITION (n = 133) and GERAS (n = 417) patients were observed for changes in cognitive, functional, neuropsychiatric and HRQoL outcomes. Least squares mean (95% confidence interval) change in caregiver time (hours/month) spent on instrumental activities of daily living (iADL; 29.22 (19.16, 39.27) versus 3.20 (-11.89, 18.28), p = 0.001) and supervision (66.59 (47.49, 85.69) versus 3.04 (-25.39, 31.48), p < 0.001) showed greater increases in GERAS than EXPEDITION. In the sensitivity analysis, changes in neuropsychiatric and HRQoL scores and caregiver time spent on basic ADL were also significantly greater in GERAS than in EU/NA EXPEDITION patients. Conclusions: Patients with mild AD dementia participating in the EU EXPEDITION RCTs and the GERAS observational study showed a similar decline in cognitive, functional and neuropsychiatric symptoms over 18 months, whereas changes in caregiver time measures were significantly greater in GERAS. Results indicate the importance of using similar regions when comparing real-world and RCT data.